I Have Been Sexually Active With My Boyfriend For A

I have been sexually active with my boyfriend for a year and a half. I'm 28 and I've never been pregnant, we aren't trying nor or we preventing (no form of birth control). I often ask if "I'm ok in there" when I see my gynecologist and the answer is always yes I'm fine. I have a feeling that I'm not fine. My periods were irregular for the first year (a total of 4) and its finally semi on track and its shorter. Should I ask for a ultrasound to ensure nothing physical is preventing me from getting pregnant?