Congrats on hitting 15 weeks! I too am 15 weeks and have had the same feelings at times. My first doppler at 12 weeks did'nt pick anything up! Freaked me out, a scan revealed bub doing sommersaults and moving around far to much to hear heart beat on doppler. I have heard heartbeat at 14 weeks and it too was faint but it was there and a healthy range. We are in a hard stage now because the symptoms are fading and we can't feel bub move yet, but we wont be far off. Best wishes for you and bub!!!