Body can't handle exercise?!

I've been living a pretty sedentary lifestyle for about the last 5 years and just recently joined a kickball league to get back into shape the "fun" way. For reference I'm 5'3" and 130 pounds. I'm not overweight by any means, just incredibly weak from lack of exercise. Practice is 2 hours once a week. No biggie right? The first practice I maybe sprinted around the base twice and jogged after the ball. Nothing too intense but I nearly passed out from light headedness and couldn't seem to catch my breath. The next 3 days, oh my god...i literally couldn't get out of bed. I had to use my arms to position my legs to stand up. It's day 5 now and the tops of my thighs are still pretty sore but I can walk around now.

My question is, how do I prepare myself for practice? I don't want to be sore from additional exercise before every practice but I don't think I can handle the muscle pain after what I think is a pretty low intensity workout. I stretched for about 5 minutes before my first practice but I'm not sure if that helped at all.

I'm worried because the real games start mid September 😨 I hope I don't pass out and die lol.