10 days missed period has this ever happend to you ,you tought you were pregnant but was not?

i was suppose to get my period on the 7th or 11 of december and now its december 21 and still no period but then again i am verty irregular could i be pregnant i mean i dont have any symptoms of it i just feel like throwing up but sometimes i feel that im so paranoid that is just my head making me think i wanna trhow up ....i had couple of time last month and well my boyfriend came in the condom then took the condom off and wiped everything off than he waited for 20 mins and put it back in me we always do this and i never get pregnant ...im really freaking out .please help have you ever gone trough this and was not pregnant.?