Racing Heart Rate

Has anyone dealt with a racing heart rate/shortness of breath during their pregnancy? I was in the ER on Mother’s Day after I went to urgent care due to shortness of breath, I had two EKG’s performed, and ended up doing a CT scan of my lungs to check for clots, a long with a ton of blood tests. Everything came back negative. My heart rate is reaching 135-140 bpm every time I get up, and my resting is sitting right around 110. It makes it so hard to do ANYTHING! I seem to have days where I do better, and some where I can hardly walk across the room without huffing and puffing. I had a cold when I went to the ER, and they diagnosed me with a UTI, so they attributed the heart rate to the infection, the cold, and being pregnant. Two days later, my OB couldn’t detect the infection, and I no longer have a cold. So I’m extremely confused as to WHY my heart is racing so high. Has anyone else had this issue?