pregnant or just late?

so my period comes every month & i haven’t ever been late before. i started my birth control again 2 months ago & i know it takes 3 months to start working. me & my boyfriend have been having unprotected sex, and my period is now 12 days late. i’ve taken a couple tests, and they all say negative. is there some way it would show up negative but if i got bloodwork done it would be positive? im having symptoms like i’m getting my period but it hasn’t come. any feedback would help😅