I'm a current PA student, so feel I can help you with some questions. PAs practice medicine in all medical specialties including OB/GYN, so you could certainly pursue the PA path. Take a look at this link from the American Academy of PAs on steps to become a PA: https://www.aapa.org/news-central/2018/08/6-steps-become-pa/
You could certainly major in chemistry, and not necessarily premed, to qualify to apply to PA programs. In fact, you can major in anything as long as you take all prerequisites courses for the program(s) you want to apply to. Let me know if you have any questions.