how to tell him parents that im having sex

ok so my boyfriend and I have been dating for about 6 months.n we have been having sex. im 16 and hes 18.were both a little scared because just a couple days ago we both decided to bearly go and get some birth control pills.as soon as I got them I put them on my bag and went home.but the day before we had sex and we didnt use protection since im still nt on birth control and we didnt have condoms we just let it go .but the next day after I got home with all the birth control pills and some after morning pills I decided to take a pill.while I thought my mom was sleeping I took out all the pills to put them away but then my mom walked in on me and saw me with the boxes of pills. she tripped out and I lied sayin I got them at skoo and after talking to my boyfriend he told me to talk to her and tell her the truth with out saying that we have been doing it.basically I told her that me and my boyfriend went to planned parenthood and got some birth control pills .after I told her she accepted it but now she assumes that im going to tell my dad otherwise shes going to be the one tell him.but the thing is that im scared to tell him just imagen,they all ready know im not a virgen and after they found out I promised I wasnt going to do that again,but it was hard not to.they think my boyfriend is the best and they like him a lot but my consequenses from last time went on for 6 months I couldnt see my ex boyfriend nor go out the house and I got my cellphone taken away and just the worst things ever.n im scared that if I tell my dad all this will happen again even tho were thinking about telling him that we just got them to prevent any preg if we were to do it,thing that we have all ready done. what should I tell my dad?.if I tell him the truth that we have he will send me to mexico and will not let me see him again.n if I lie they probably wont belive me and I will still get grounded or something .what do you think he will do ? im just calm and thankful that my boyfriend has the guts to come and talk to my dad about the situation too.

please help me …