Most common women’s infertility issues?

What are the most common causes for infertility in women? We’ve been TTC for 7 months with no luck. I’m 25 and my husband is 26. My husband got a SA recently which came back good. I’d like to get tested, too, but I don’t know where to start. For reference:

-I have 28 day cycles like clockwork. I have literally never been even a day early or late.

-I get a strong positive opk on CD14 each month

-I get plenty of EWCM every month during my fertile window

-I (and my husband) are at a healthy weight and eat pretty healthy

I’m seemingly fine, but what should I test for first? I do get occasional pelvic pain (nothing crippling though) and have frequent diarrhea. Not sure if that could be affecting things.