Anyone else have irregular periods?

Hi ladies! Is it just me or does anyone else have irregular periods? And by irregular i mean is your period ever 2-3 weeks late? I’m also a lil underweight too..I’ve been on birth control for maybe a year. I got off it about 4 months ago and I’m now taking the pill again. Maybe that has something to do with it but my doctor thinks I should get a pelvic exam to make sure I don’t have lupus..? Anyone else relate?