Why do i feel weird when i kiss?

Whenever i kiss someone, being my boyfriend, i always get this weird feeling that i shouldnt be here..like its not right. i talk to my friends about this and they think im just alittle koo koo lol. i told them i should just go for a day and see if thats it cuz i swear! no one should feel this way when they kiss their boyfriend..like when im away from him i get soo lusty for him and want to kiss him and have and all that but once im with him i dont feel like it. and when i think about kissing him when im with him its like, "ehh i dont want to, grosss.." and i think hes attractive so idk wuts going on..