Boyfriend doesnt want anymore.?

ok so im 21 and my b.f is 37. We been dating for over a year... been knowing eachother going on 2 !!! Whe we first hooked up we had like 3 times a day. Lately its been once every 3 days. Im young and i wanna FK !!! My boyfriend has been acting really strange though, and i asked him about it , he gave me some b.s azz excuse. What should i do ? Is it me.... or him ???