short acting medication advice | ADHD Information

Here's the short version: I am in college. Have a busy course load and am fairly dedicated to getting good grades(silly not to be for how much it costs). I have taken medication since I was about 11 with breaks here and there. Tried mostly all the adhd meds at some point. 10 different ones total I think(if you count the short and long acting ones as different ones).

I take focalin short acting 10 mgs once to twice a day depending on homework and stuff. Every once in a while I take it 3 times(doc said that is okay). I prefer short acting because it fits my weird college schedule best. Don't like ritalin short acting, took adderall short acting for a while but haven't in a long time. Never tried dexedrine. Here is what I am having questions about.

1. How long does short acting adderall usually last and take to start working? How about dexedrine?

2. Has anyone tried dexedrine and what is it like. If you know any info on it I would appreciate it.

3. Focalin is the one I have taken the most often over the years. I feel like the 10mgs isn't working as well as my other meds I have taken in the past did. Maybe I have a tolerance. So should I talk yo my doc about 15mgs? Do they have a 15mg pill or do you cut one?

4. What is the 10mg of short acting 2x a day equivelent for the others. I usually take about 20 or 25mgs of focalinxr, took 60mgs of vyvanse and 36 of concerta. Is this a less strong or more strong dose than those? Is 15 usually a high dosage or normal one for an adult?

Okay sorry for all the questions but I just really want to find the one that works best for me. ANY advice appreciated :)