Racing heart

I’m a first time mom at 18 and I’m so excited but I have no idea what is normal compared to things that I should worry about. I’ve been pretty active my whole life but I’ve definitely gain wait from the baby (15 weeks) but recently I can’t do any things like walking at the store, standing in the check out line, to even just standing doing a clients hair without my heart starting to race or feeling like I’m going to black out. I have a doctors appointment this week but I just need to know weather I should be worried or not!