Can Contraceptive Pill Affect Result Of A Pregnancy Test?

I am on the contraceptive pill..i had a period about 3 weeks ago but i think i may be pregnant, i don't have any signs of pregnancy apart from pains in my stomach. I saw my gp the other week and they did a urine test (this was a new patient medical) it didn't show that i was pregnant but i didnt ask them to pacifically test for this. would it have shown up anyway and can the contraceptive pill affect the result of a pregnancy test