I'm pretty sure breastfeeding has something to do with this, but it's driving me crazy lol....…

I'm pretty sure breastfeeding has something to do with this, but it's driving me crazy lol.... started my period last Monday, almost 2 weeks late.... it got progressively heavier for 3 days (Tuesday Wednesday and Thursday) was a normal flow Friday and Saturday.... very light sunday..... have felt completely off the past couple weeks, nauseous crampy (after my period) etc...... have taken 2 pregnancy tests, even tho I had a tubal because nothing is 100% and I know someone who got pregnant after having one, both negative..... what is the deal???? Like I said I am going crazy lol I have been exclusively breastfeeding for over 8 months so could that be it?