I used to get pea-to-marble-sized bumps at the hairline at the back of my head. They would come and go, and sometimes they were painful. But by the time I got around to getting a doctor's appointment., they had usually subsided. That is when I started keeping a log of when they occurred. For me, they always occurred around ovulation time. I finally asked my doctor if I could just pop into the office the next time they appeared, without an appointment. When he looked at them he was not concerned. I had them off and on for about 10 years. I am now 58, and every now and then, usually when I am surrounded by younger women like when my daughter is home from college, I will get a bump or two. The reason I am responding is because I never really discussed this with my daughter (who is 22), but she called last night because she "has a few of these strange bumps on her neck at the hairline..."! I would also add that most physicians seem to disregard problems that seem to occur in sync with hormonal fluctuations, as well as side effects from medications, like birth control (effects on mood swings).
MY SUGGESTION: I suggest tracking when they seem to be inflamed (painful) or seem to swell, and just compare that with your ovulation/menstrual cycle.