2nd trimester symptoms ?

My second trimester was smooth. Even first trimester was fine. Not much nausea and vomiting. Currently I'm third trimester and it's very tiring. I have difficulty in breathing now. I feel choked when lying down. My heart rate goes high too. How is your tummy size? I didn't have much tummy until recently and I feel all these uneasiness started after my tummy grew. Now I find getting out of bed itself as a major task 😀 I'm like that tortoise who feel on its back 😆