Need help asap! WHAT IS GOING ON?!

Ok so here it is....

Today has been a strange day for me i thought I was pregnant... so I did a pregnancy test n it came back negative though however I only had sex about 5/6 days a go so if i was pregnant I dont know if the test would pick it up

But today my mood had been crazy went from being kinda neutral most of the day over the past 4 hours I have been so angry and frustrated that I haven't been able to sit still... i could feel that I wanted to cry I dont know why! But I couldn't cry then eventually I started to relax a little and started crying for about 30 seconds then I was fine i dont know what all that was about...

i have had slight cramping in my lower stomach and needed to go to the toilet so much it's annoying!

Can someone help me! I have been pregnant before and these are the symptoms I had when I was pregnant but the rest I did today was negative... help?!