The only tip I can give you is to be resilient and willing to learn. It is very beneficial for you as you can learn a lot of soft and hard skills over time. And when you move over to another company next time, you will be more than capable to do your job efficiently.

I have been in a startup for 3 years now, at first also struggling a lot but the really good thing about startup is you grow with the company and the work you do can really have huge impact. If you feel overworked, its OK to ask for a break to recharge. No matter what type of company you work it, burnout can happen if you don't take care of yourself.