Any tips or help?

So I’m about 19ish weeks pregnant, we’re unsure because I haven’t had a period since when I got pregnant with my son (who’s almost 1) so the OB is guessing right now until I get my ultrasound on the 25th.

ANYWAYS, my heart will randomly start beating super hard (like moving my body and chest/shirt hard) and really fast. This isn’t the first time it’s happened, it happened a few months ago before I found out I was pregnant. I will also get SUUUUPER lightheaded if I stand for more than a few minutes and feel like I’m going to pass out, no matter how much I rest or how much water I drink.

I’m a little worried but I’m really unsure what to do.