12 weeks pregnant but suddenly don't feel preg

I'm 12 weeks now with my first child but suddenly all my pregnancy symptoms eased up. I don't feel so nauseous anymore. I feel more energetic and I can eat better. The lack of symptoms makes me worried that I'm not pregnant. Is this normal? I do get the occasional tailbone pain still. It comes in waves, probably due to the release of hormones every now and then. But otherwise, I really feel OK. OH, and I sometimes feel abit crampy on my uterus muscle. Feels like sometimes a muscle has been stretched... That kind of sensation but it's not painful. Should I be worried??! I can't help but to feel worried.