3+ months postpartum and something is right???

Hey moms I’m over three months postpartum from my second baby with my first it was a long 18hr labor but normal delivery no tearing and I got my period back within about 5-6wks this delivery was even better I was in labor (induced) for about 5hrs, pushes for about 3min and no stitches r any problems and I was back to myself in about 3wks but I still have not had a period I bled really light for about 2 days and that’s been it I’m also feeling very nauseous all the time also having some belly pain and kinda lightheaded...I have taken pregnancy test just in case and as I suspect they were negative any ideas of what can be wrong?