No idea what to do..

I have very crazy periods. sometimes they will come every month, sometimes they skip a month or 2 altogether (which is what is happening right now - last one I can remember was second week of February) Okay, fine, I can deal with that. But, this time is different, because I have been having pregnancy symptoms. Fatigue, increase in appetite, general nausea, nausea after eating, cramps (left side mostly but also center - for about 4 days, increasing in intensity as the days go by). Not sure if this is also a symptom, but my nipples have been erect for at least 2/3 of the day for the past 5 or so days as well, and only slightly tender to the touch (but i have sensitive nipples as it is, so cant really rely on that). I've taken 2 First Response HPTs already. first one had a positive but it disappeared as the second test line appeared. second one was just a bfn. Any advice?