What Causes Severe Pain In The Calf Muscle?

Hi. Two days ago I woke up from a nap due to severe pain in the back of my calf. The severity of the pain was decreased within 10 minute but still hurt just enough to be painful to walk on. My calf still continues to hurt although it is more of a sore feeling now. In addition to all this, it is 3am and I m awake due to the feeling of vomitting. I m not quite sure if these are two separate cases or if they are linked. I also am a bit worried that it might be due to pregnancy. However, I just had my period last week and had sex friday, saturday, and sunday of the following week. If I were pregnant, wouldn t it be extremely early to be showing signs? If it helps, I m on birth control for my 3rd month.