Help me! My calves hurt so much after running!?

So today I had swimming in the morning for two hours, which went very well and was perfectly fine. However, afterwards I went running for about a mile and a half afterwards. (about 20 minutes break in between.) I haven't done any running in a LONG time, but I still did the whole thing nonstop. About 3 minutes after I was done, I went to sit down and then my calves started cramping up really bad, like so bad that I tried to stand up and i basically fell back down. I could barely walk and had to "hobble" to the car. I was going to bike home, but I probably wouldn't have even made it to the bike. When I got home, it was worse. I had to take a shower sitting down. Not. Fun. So can somebody tell me what is going on? It feels kind of like my leg grew and the muscles inside shrunk, so every time I stand up, it is extremely painful. Sorry for making you read all of this, I just want to add detail and what not...Thanks!