Experimenting with doses

Hey guys. This is my first post. My doctor is not very cooperative or open-minded when it comes to dosing, and I understand where she’s coming from because maybe my situation is abnormal or my body reacts weird to the meds. Basically my situation is this: my productive days are very long (I go to college full-time and I work full-time to support myself) so a normal productive day for me is about 7am to 10pm, which is ~15 hours, which is what is making it difficult to figure out a dosing regimen for myself.

Basically Vyvanse lasts about 6-8 hours for me, roughly. My doctor is not willing to prescribe it twice a day, and from what I’ve read, it’s not supposed to be prescribed twice a day, so that’s fine. As of now she also does not want to prescribe an IR booster because she believes the longevity issue is due to the dose of Vyvanse being too low. She IS willing to either 1) change to a different medication altogether or 2) increase the dosage.

My problem is that even though it’s not lasting very long, I seem to be somewhat sensitive to the medication because even 20mg feels too strong for me (but too short lived). I told my doctor that my main concern was that it did not last long enough, but that 20mg was strong enough, or even too strong, and her response was to increase me to 40mg, claiming that I’d get used to the stimulant effects and it wouldn’t seem too strong after a few weeks, and that the 40mg would make it last longer.

I’m honestly scared to even try the 40mg I just picked up because I’m not joking when I say 20mg is too much, so now I’m planning to try to ‘experiment’ in the sense of dosing myself by emptying the capsule into water and trying perhaps 10mg twice a day. Has anyone done something similar or come up with a better alternative? Is this the wrong medication for me? Is mixing it with water the best way to split doses yourself?