Why am I so nervous at church?

I walk in and they do the singing thing. I sing along and i am feeling it but then it never stops. I feel as though I have to fake being happy or bobbing my head. Im 18 and I just started going for 2 days now. People are like, AMEN, JEsus Jesus! and it makes me feel uncomfortable and not human. We sit down a short time after many many songs. I get tired and I just want to hear the preacher preach because thats what i am there for. I feel so uncomfortable though I bite my lip and stare in space. I have talked to the kids my age but they are like robots. Help me please? I love jesus and this is ruining my faith and I don't know why. My mom says there will be a lot of singing in heaven but how are these people so happy? I don't want to upset god.