Its totally fine. Im the same hehe
The sperm softens your cervix, the orgasm can start contractions. If you're not ready you won't go into labor. Trust me, I've tried lol.
Yes, it is okay to masturbate.
I think most of the trigger with sex has to do with the sperm actually softening the cervix.
Most women say it doesn't make a difference unless your body is ready for labor anyways.