Welcome. You will find plenty of help here as well as a lot of moral support.
A few things, some of which have already been said:
1) Get your hands on "The Explosive Child" by Ross Greene. To get a bit of an idea, have a look at the discussion of this book over on Early Childhood. It's sticky, so will be at the top of the forum. The book is a big help especially for kids with oppositional behaviours, regardless of the cause or the diagnosis. If you can't afford to buy a copy, get it out of the local library.
2) I also think there could well be more to your son than just ADHD. That isn't necessarily bad news - sometimes getting answers that make sense can also open doors to getting help, especially help that needn't cost a fortune.
3) Try to keep in mind - somewhere in there is a good kid who is incredibly frustrated and confused by a world that doesn't make sense and which is overloading him at times.
4) The bedwetting - it's quite likely that he really doesn't have as much control here as you think. There can be so many factors, not the least of which can be some degree of sensory integration problems. Rather than perhaps needing a head shrinker, he may just need patience, observation, support and a helping hand especially if you can wait until warmer weather. A lot of us have been through this. We went through it with both boys, in one way or another. Neither of them found it easy to recognise their body signals that told them when it was time to go to the toilet. For years after he finally was toilet training, difficult child 1 would need reminding for bowels frequently. He would literally forget to go. difficult child 3 was still not properly toilet-trained when he started school; I often had to go to the school to clean him up. This isn't too uncommon - there were a few kids I encountered in my volunteering at the school who had this problem. From time to time they had an "air" about them, if you know what I mean.
Bladder training - difficult child 3 was dry during the day, he never wet himself at school, but he would ALWAYS wet himself at night, floodingly so.
So here is a tip that you might be able to try now - I presume you have him in Pull-Ups or similar? Try putting cotton underpants on him UNDER the Pull-Ups. He should be able to feel when he's wet. A big part of the problem is that often they just don't recognise as easily, when they're wet. Especially if they sleep really soundly, which some kids do (especially the Pervasive Developmental Disorder (PDD) or ADHD kids, who are utterly exhausted mentally by the end of each day). Pull-Ups and similar disposable nappies are sometimes TOO good at their job of keeping the child dry next to the skin. Putting underpants there can put back the feeling.
The other tip is to introduce "toilet time" at several times during the night. The best times to do this are at the child's bed time, then again later on at YOUR bed time. If you can, introduce another one early in the morning. Don't let him wake up and then lie around in bed; often they need to get to the toilet FAST on waking. One young girl I know (classmate of difficult child 3's in the earlier years) would be dry all night, dry on waking, but would wee into the nappy instead of the toilet, out of sheer laziness and habit. All the mother had to do was simply stop using the nappies, and the little girl never wet the bed, she just went to the toilet on waking.
There are other things you can do - alarms with pads, for example. A tip again - a lot of people put a plastic sheet under the bottom bedsheet. We didn't use plastic because it makes a loud, rustling, crinkle sound. We bought some vinyl fabric (it's cheap to get good stuff) and used a sheet of vinyl instead. Once the child no longer needs it you can use it to re-cover chairs. Or we use it in the car in summer, to put under children and adults who have just been for a swim and are still wearing wet swimsuits.
Nothing gets wasted!
Your child should have a thorough evaluation, they take hours and hours when done properly (so the diagnosis isn't just given after a one hour initial consult). This of course costs money, but if you never spend anything else on your child's care, a good and thorough diagnosis is vital.
We've had to muddle through a lot ourselves, partly due to poverty but mostly due to lack of services in our area. As a result we've learned a lot all by ourselves and despite the lack of big bucks spent, our kids have done/are doing well. Not without hassles at times, but the people on this site have been very helpful to us, and in return we (husband & I) try to help others.
husband first used to "lurk" here, mostly to see what I was writing about, and later because it helped hi also get a good idea of what to do. He's since joined in his own right. We thought we were communicating really well before; it's even better now.
So again, welcome.
Marg