Miscarriage in the second trimester?

Dee
I haven't had one yet but I've been worried.... I engaged is some pretty tough sex on Sunday and has a very tiny amount of blood afterwards (about a streak). Since then I can't find a heartbeat on my Doppler and I'm not sure if the kicks have been else where but I haven't felt any since then either. There has been plenty of people that have told me that sex cannot cause a miscarriage but I'm extremely worried. I can usually fill a kick or two a day if I feel for it and I'm about 50:50 if my boyfriend felt kicks or not yesterday. I guess I'm just worried and I'd hate to call my doctor over this and nothing is wrong at all.... I guess I just need assurance or a peace of mind... Any advice? 
(I still have my symptoms and get flutters mainly when I just wake up)