Help!!

So im worried about my period. I skipped a period for 2 months. I had cramping, i was feeling nauseous, headaches. Me and my husband thought we were pregnant but i took a pregnancy test and it cam back negative. So now i started my period and usually it lasts 4 days to a week. But ive been on my period for almost 3 weeks now. When my period was late before it was because of stress and usually will be late for the most 15 days and when it came it will last a week. But this time its diffierent. I asked my mom to see if she knew what might be going on and she said she didnt know (she doesnt like talking about these things). Does anybody know what might be going on??