There's likely a hormonal shift going on as your body readjusts to not having the pill. Does it hurt or burn to pee/are you going a lot and not pushing much out? You may also have a UTI.
The first question: had you sex without protection?
The second question: If you had sex without protection, the boy finished inside you?
If you answer the two question with a yes, the pregnancy is a possibility.
So when was/is your period due? I have been in a similar situation where I get myself so worked up, even though I know I have followed all instructions correctly and that the chance of pregnancy is so slim, I think it is natural to be scared, especially when you first start having sex etc. If I was you, I would take another test a few days after your period is due, if this has already passed, I would maybe go to your GP and have a test done there just to put your mind at ease. The chances of pregancy are very unlikely but it can take a while for your period to re-adjust after coming off the pill and you don't want to be panicking and not knowing for weeks on end. I have also found that the more paranoid you get, you can actually create symptoms in your head and make things you would usually ignore seem a lot more intense.. it is crazy what the brain can do to the body and what worry can do. Just try to relax and go to the GP if you are really worried - it's the only way you will know for sure!