I had my period on March 1 and I usually have a 28 day cycle. I was supposed to get my period on the 29th but I was late. I stated to bleed on the 31st and it was pretty heavy and I had terrible cramps like I usually do when I get my period. Today, the bleeding is very slight and I am nervous that I might be pregnant. I took a first response pregnancy test the morning after my missed period and it was negative. I also took another test today which also turned out to be negative. Im concerned because I feel like I have some symptoms (headache, dizziness). However, since my last period my bf and I have only had sex twice and both times we used a condom and he pulls out before ejaculating. Is it possible that everything I am experiencing is the result of stress or could I possibly be pregnant? please someone help

..one more thing, is it typical for implantation bleeding to have bad cramps and heavier bleeding like a normal period bc that is what i was concerned that the bleeding might be??