Why has my butt muscle stopped working?

I was hit by a truck while riding my bike and broke my back. My right butt cheek was also super bruised and swollen for 2-3 weeks. Its 2 months later and my butt cheek looks fine, but I noticed the other day that the top muscle doesn't work at all.

I can flex my butt cheek and only the bottom muscles will flex not the top. It's really weird. The muscle that won't flex feels a little sore when I poke it/massage it. My butt cheek visually looks different while relaxed too, which probably means that the top muscle has atrophied due to lack of use. I'm assuming the top muscle took the majority of the impact since the lower muscles work fine.

I would go to a doctor but have no money, no insurance, and massive amounts of medical bills already from this accident.

What's wrong with my muscle and how can I fix it?

Thanks for the help!

-james