I've recently been prescribed 15mg of adderall instant release for my ADD. I'm 19 year old, female, college student.

I've been taking the adderall for about 2 and a half months now and find that it usually kicks in after about 20 mins and I only feel the effects for about 3.5 hours, 4 hours if I'm really lucky. I have heard that the average time is around 5 hours or more. Why do I only feel the effects for such a short amount of time?

Also, does anyone take more doses of adderall on days that they really need it? Some days I have a huge workload for school, so I wake up earlier and stay up later studying, or doing homework; thus I take more doses... usually 3-4. Other days when I do not need my attention at 100% for a long period of time I usually only take 2 doses. This is usually when I don't have much homework or on the weekends. Is this unheard of? And is it okay for me to do?

For anyone that thinks to recommend Adderall XR as a solution: I do not want to be put on an extended release drug for ADD. I have taken them before and have had bad reactions. I also like to control how many hours the effects last; hence me taking different amounts.