Can't breath and pelvic pain...

Starting from late in the first trimester early into the second, I have periodic episodes where I feel as if my baby is stretching and taking up my lung space leaving me feel like I can't breath... Now at 26+5 I am starting to have the same separated pelvis (sp) pain I had with baby #2... But back then, it started right at 3 months and it left me unable to even walk very much. I have a 5yo in kindergarten and I have to go make sure I get him to and from the bus stop mon-fri and with a SP I've been told it's best to try and avoid stairs as much as you can but I live in a walk up apt... All of these things make me worried about the last 3 months.... Any advice or just positive encouragement welcome. Thank you ladies.