Training hiccup!

So this morning was my second week, second session and well, it didn't go so well. I was supposed to run for 25 minutes...I ran for 10.5 minutes and had to stop and walk because my knee was killing me! I've never suffered from knee problems before and yesterday my knee was fine so I don't think I hurt it on Sunday when I ran...I'm guessing I twisted it yesterday some how as it was slightly sore when I got up this morning. So I pushed on and managed to run a total of 21:30 minutes but I'm beginning to think I shouldn't have as I'm in absolute agony now! So, tonight when I get home I'm going to ice it and rest it and wrap it and not run again till it's feeling better. I'm so frustrated as I'm sure I would have been able to run at least 15 minutes without stopping if not the whole 25 minutes if it weren't for my knee!