What can I do 4 extremely painful thigh muscles after 2 days of very strenuas exercise. I can barely go up my stairs or sit/squat?

Overuse thigh pain. The nih advises: if you have leg pain from … overuse: rest as much as possible. Elevate the legs. Apply ice up to 15 minutes 4 or more times a day. Gently stretch & massage cramping muscles. Take otc NSAID (advil/motrin/aleve etc) or tylenol (acetaminophen). Drink plenty of fluids, especially those with electrolytes (potassium, magnesium, sodium); eat healthy meals with lean protein to aid muscle repair.
Avoidance is best. It is best to avoid doing strenuous things without building up your strength first. Now that it's happened, you can take Ibuprofen or Naproxen for pain and inflammation, eat plenty of protein to help your muscles repair themselves, and drink lots of water. Also do some gentle stretching and try to keep active with a little walking or swimming.