So out of breath!

Before pregnancy I was 127 pounds and reasonably active, at 25 weeks I'm now 134 pounds but I find that ANY form of physical movement takes my breath away and elevates my heart rate? Sometimes even getting up and walking to the bathroom/kitchen, or climbing one flight of stairs. I drink a LOT of water, get a good night sleep, am on supliments for vitamin D, B12 and iron defficiency but I'm still struggling for air after simple tasks. It's been like this for about six weeks. Is it just carrying the extra weight? What else can I do to fix this? Do I need to exersice more? I'm barely doing anything currently but even walking short distances results in 15 minutes of recovery.