Not really feeling baby

S

So I'm due May 30th which makes me almost 14 weeks. I had an ultrasound done at 9 weeks, everything was good, heartbeat was 158. At my 12 week app, they found the heartbeat for a split second then lost it and spent the next 15 minutes poking around my belly. When they did find it again, it sounded faint/far away and said it was reading 159 bpm. I felt little flutters a few times a few weeks ago but haven't felt much lately, and don't feel like I'm getting any bigger these past few weeks. Am I just worried over nothing? I keep feeling like maybe I've had a missed miscarriage. I don't have my next month app until December 11th and the gender scan is Dec 26th. I'm going crazy here! Anyone else feeling this way? This is my second child.