3rd trimester problems. Please help!!

My baby boy is due October 1st. I am so excited for him to be here. I have a 2 year old daughter and I am a SAHM. Lately I have been so dizzy and short of breath and nauseous. I started throwing up again like in the 1st trimester. I can barely get anything done. Even sitting up right for a while makes me dizzy and I feel like I can't breathe. I almost constantly feel like I'm gonna pass out (which has happened a few times). I am exhausted and frustrated. All my tests have come back fine, which I am so happy about, but I don't understand why these symptoms are so extreme. Is it gonna be like this until I give birth? I had a few of these symptoms when pregnant with my daughter but nothing like this and they went away. I just don't know what to do anymore. I feel like a lazy mom/wife and it's weighing on me. Any advice is appreciated. I want to get things done but the more I push it the worse I feel and the more likely it becomes that I will pass out.