hi, I am on a birth control pill that makes it so my period comes once every three months. I haven't missed a pill once, and I had intercourse last night, my partner came inside of me, and now i am worried. Plan B only works 72 hours after intercourse, but is also $60. as i am a struggling student, that's a bit to spend! since i obviously don't want to wait another 3 months to find out if i am in fact pregnant, when can i take the hpt for it to be effective? thanks.