I can't excercise!

So I'm very out of shape and I feel like I let it get too far to the point where I can't excercise! Whenever I try to excercise I get extremely out of breath so quickly, so badly my chest hurts and I feel like I'm going to throw up. And also I start to feel like I'm going to faint. I can get through little excercises like 20 jumping jacks, squats and a plank, and maybe 4 girl push-ups but even those kick my ass! I have 0 energy all the time and my strength doesn't match my size. Like I'm really fat but I'm like weak. Like I can't or win in play fights and like if I try to grab a text book with one hand at school I can't, I have to use two. How can I get stronger, and get through excercise?