Small red and sore bumps on lower left leg, pain in calf area and hurts to walk, only left leg only?

Pain in calf: that makes it difficult to walk is definitely something you want to have looked at by your provider! The rash may or may not be related. Deep vein thrombosis sometimes present with pain in the calf region as well as swelling, warmth and redness. Get it physically looked at for a definitive diagnosis!

Check the Bed.: Whether or not the small red bumps are related to your calf pain remains unclear. It could be totally separate from the bumps. Small painful red bumps, especially on the calf area are highly suspicious of insect bites and reaction to their injected protein. Bed bug bites are described much in the same way as you describe them. When in doubt, check it out.