Your complaints are the signs of inflammation. That could be a delayed onset of muscle soreness (DOMS) or micro tear of thigh muscles due to overuse..
You need to give rest to that left thigh immediately at least for 2-3 days.
Apply cyopack every two(02) hourly.
Take some nonsteroidal anti inflammatory drugs (NSAID
Keep a pillow beneth the knee while sleeping.
Wish your thigh would become symptoms free soon....