I used to take a short acting ritalin that made me do the same, and I'd crash before the end of my day almost everyday. It was really frustrating, so I talked to my doctor about it and he didn't seem to really care? He just kinda said that's a side effect and it happens and that there's not much he can do about it. However I then asked if I could change my doctor and the receptionist said I could talk to a nurse about it instead, and she's been way more helpful, understanding and informative about medications and when to try something new. She put me on some extended release Ritalin so that it'd last longer in the day, plus a small dose of it to take again if I'm feeling like I'm going to crash before the end of the day again. It's really helped, although I'd say be careful about it because it makes your heart race and if you don't take it with food you'll feel sick. But that's with most of the meds they prescribed unfortunately. I hope this helps