I really dont know Im sorry! This may be silly but who told you that you were 2-3 weeks pregnant? Its just becuase I read somewhere and it couple be completely wrong that when you do a pregnancy test its generally assumed you are 4 weeks pregnant, again I could be wrong about that. So if you are saying 2-3 weeks because thats when you did your test then you could be further along than you thought!!
I dont want any of that to scare you as it coupld be wrong, im sure someone on here will be more help.
But you could be experiencing an ectopic if you are having pain down one side. i dont say that to panic you.
but my advice would be if you are worried and in pain seek medial help. good luck
xxx