Yesterday I was in the supermarket and I squated down to get something on the bo!

This problem is very common, you just pulled a muscle nothing to worry about, it will hurt for a few days and as far as your headache you probable just have a headache. I don't think its anything serious but if it persist go see a doctor. Your headache could be from your sinuses, or just from the pain in your leg can cause a headache. Relax your going to be ok, the more you tense up the worse your leg is going to hurt. Massaging your leg is good, if there is swelling don't use heat but use ice. If no swelling get into a warm bath and soak, the heat will start to relax your muscle and make it feel much better. Also ibuprofen will help with the pain and it's a anti-inflammatory and will help with the swelling. Hope you feel better soon