Knee pain--due to fall or overuse?

I am still new to cycling and am not sure if my knee pain is because of overuse or injury. I rode 30 miles on Saturday--10 to get breakfast and then 20 back home. (We took the scenic route). On the way home I had a minor fall. I unclipped one foot at a stop light, but then leaned the wrong way and fell. I hit my elbow and knee. They are scraped but nothing major. Got up, finished the ride. Then on Sunday we did a similar ride. 10 miles to breakfast and 17 back home. Now the back of my knee is hurting a lot. It hurts mostly to bend it. I'm just not sure if it's hurting because I rode 2 days in a row or because I fell. I had lateral release surgery on both knees 6 years ago, but cycling is one thing that usually doesn't bother my knees too much. (except for big hills and standing to pedal). Any thoughts? Do I let it be for awhile or see a doctor? I've been taking Motrin and it isn't doing anything for the pain. It was really hard to sleep last night--just couldn't get comfortable. Thanks!!

I actually haven't had the bike fitted professionally. We got the bike from Craigslist and just got a new seat for it. The original owner had put a gel seat from Wal-Mart on it, so we got a Bontrager this weekend. Also getting a shorter stem. (I have a 56cm bike because of my long legs, but need a shorter stem for my arms). My hands and wrists hurt a little while riding, but are ok now. I think I put too much weight on my hands sometimes, but it is something I try to be aware of while riding.

Anyway, I think I need to go in to the bike place where my husband got his bike to get fitted. I might also call the doctor just in case. Thank you!!

My doctor sent me to my LBS shop for a proper fitting when I had a numb hand after a ride. Can't say enough about getting a proper fitting!

When you go, wear your bike shorts, bring your gloves, as both of those will affect how your bike fits. Expect to spend half an hour (or more) on the trainer at the shop (you'll need an appointment for the fitting). Most shops charge something for this service, or you should at least expect to be charged.

hmmm, back of the knee pain. Used to be someone on here that could diagnose that. It does sound to me like the bike is not fitted right. Maybe the saddle, the handlebars... need to be repositioned.