I went several years on birth control after my 2nd son was born. That birth control medicine really screwed up my periods. I would go months without having one, and then go with having them. It got to the point it was making me so sick I had to get off of them. Well once I got off them the doctor told me I had a year before my body would completly adjust. Well I went several months doing ok, I woke one morning to being so sick to my stomach I thought I had the stomach flu. Well as the day and weeks went by I started to feel fine, except for my breast were VERY tender.
I hadn't had a period in almost a year by this time, so I figured there was no way I could be prego, again! I took several, like yourself, pregnacy test, all of which came back negative. I just finally decided that my breast were tender and I wasn't going to get my period. Well a month went by and they just kept getting worse and worse, so I finally called my doctors office and talked to my nurse. She told me to take a pregnacy test, I told her i had, I had taken several and all negative. She asked me how long ago, Told her a month. She insisted that I take another one. Well I went and got another one and it came out positive. After getting an exam at the doctors office a week later I found out I was a month and half pregnant.
I know it seems like a long story, but my point is this. Just because you don't have a period, or because you do have a period, don't get your hopes up. And like one other person said, don't stress about it. Give your body a while. If in 2 and half weeks you still don't get your period, get another pregnacy test. If you read the back, most of them (atleast the ones i've seen) say they aren't very good below 4 weeks gestation.
So goodluck and I hope you get what you want soon!!!