Laying on left side problems

Des • 2nd pregnancy due Feb17'! Back to back pregnancies- first baby will be 1yr old Jan 15 💗 #teamgirls
I was told to try and lay on my left side and I used to sleep on this side no problem. No I like laying on my right. When I lay on my left side my heart rate increases and I feel like I have to breath harder. Anyone know why? Or experience similar?