Obviously you'll need to remedy the tightness and correct your posture but go to a doctor!
I have a herniated L3/L4. I aggravated it in 2014 and the disc swelled to the point that it pinched a nerve. I lost feeling in my shin and my medial quad quit working. Seriously, I couldn't flex the muscle or do a leg extension with 30lbs.
My road to recovery included trips to a chiropractor who does a lot of active release technique therapy. It's essentially tissue massage where you're tight with the hopes of those areas releasing and allowing your body to return to a balanced state. In your case they'd focus on your low back, glutes, and hips.
I think my body needed time to heal. Once the disc swelling decreased I regained my strength and the pain subsided. The tissue and strength work I did helped speed up the process.
I think your first step is to truly identify the problem via a medical professional.