Many have been there: How much damage in life is happening between suspecting it's ADHD and receiving treatment.
What I found most effective is Modafinil, if you happen to live in a place where it's considered a lower schedule prescription drug and is easily accessible. It's less safe, so follow doctor's orders and instructions carefully. Use 1/8th of a pill to check tolerance on day 1.
If you have not built tolerance to caffeine, that is effective for a couple of months as well. Consider guaraná or black tea if you need a lasting effect for many hours.
Another option is if you ever got a prescription of an anti-depressant that works off-label for ADHD as well and have some left over. Many of them take a month to work, but sometimes, the ADHD effect is immediate.
Of course, when you get your real prescription, check if you need to stop the temporary one first! In case of some anti depressants, that can be several days.