The behaviour you describe could also fit with ADHD when the medications have worn off. You can also have rebound problems, with worse behaviour for a short time after medications have worn off. My older son had rebound on ritalin but not on dex; a friend of ours had rebound on dex but not on ritalin.
We found that switching to long-acting forms of medication 'levelled out' the ups and downs of behaviour problems. But I stress - that's what worked for us. If the ritalin IS genuinely helping him, hopefully you would notice it too. But you would need to discuss this with his doctor.
He IS only 5, you've got typical boy behaviour in this mix as well. The forgetting stuff five minutes later - ADD inattentive type is also like this. Also, difficult child 1 has problems with laying down short-term memory. He also would forget. And sometimes there's a degree of self-censorship, because if they really had to live with themselves and the long list of all the things they've done wrong each day they wouldn't cope.
Kids can seem very different but have problems which are connected. And often, with a kid who is a behaviour problem, you need to find different ways to discipline and parent, because the usual ways will make problems worse with some kids.
With your five-year-old, is there any activity you can channel him into? Something he loves that will also either burn up energy or hold his attention? I used to use an indoor jogging trampoline for difficult child 1 when he was little - I would send him to do fifty jumps, when he was bouncing off the walls. difficult child 3 has a best friend who is into Lego in a big way, and invents things with them. The parents have let him have the dining table for his creations. Another five-year-old we know is into electronics and has circuit diagrams all round the house. And my difficult child 3 - if I get him to do maths work, it calms him down. It's just a matter of finding what trips their switches.
Welcome, you should get some useful advice here.
Marg