Knee Pains?

[ChristiNa]

After years of sporadic gym/treadmill usage, I started riding my bike a few days out of the week a few months ago. Then, over a month ago, I started exercising more frequently, almost daily. I started running up to 3 miles a day and doing leg presses as well as 45 minutes on the elliptical. The only problem is that I didn't have running shoes yet, just some Nike sneakers.
Last weekend, I spent the weekend at a theme park, where lots of walking and waiting in line happened- and my knees and feet started hurting very much; the shoes I wore were flat vans. Ever since I got back on Monday, my left knee has been hurting quite a bit. I can't bend it and I can't put it completely straight. I have a hard time walking, even. It's been a few days, is it possible I messed up my knee or is this temporary?