Knee pain something serious? ACL?

GiddyupTim

Glad you went to the doctor. I'm sure he got it right.
If you tear a ligament, there will be considerable play in your knee.
Here's what I know. (This, from an amateur, mind you, but one with some experience.)
People don't usually tear their MCl without tearing their ACL, and when you tear your ACL there is a loud, unmistakable pop, almost always. If you did not hear a pop and feel pain immediately, it is unlikely you tore your ACL, which means you probably did not tear your MCL.
At least not all the way on these. And, small, incomplete tears can and do heal, though some rest is often recommended.
You can google "MCL tear and test" and find out what you can do to see if you have one. Doctors will manipulate your knee, to see if there is any play in it where there should not be. You can do these on your own, comparing one knee to the other, to see whether you want to go to the doctor. When you have a torn ACL or MCL, the additional movement you get in the bad knee is usually pretty apparent.
But remember, doctors are experienced with these tests. You will not be.
The other thing you might worry about is a torn meniscus. If you have a torn meniscus, usually you will have a little 'click' (a kind of bump or slight catch, with or without sound) when you bend the knee. You will also often have a time or two or more when you will bend your knee and it will get slightly stuck and it will hurt, and you will have to slowly work this "catch" out.
Absent those definite signs, you are pretty safe in assuming that it is unlikely that you have any type of injury that needs serious medical attention. So, you probably just strained, or maybe sprained, your knee, and you are safe with conservative care and waiting.
Sometimes these things seem really serious -- like your knee has become seriously unstable and weak -- but when the swelling goes down, the knee goes right back to normal.
In the meantime, ice is your friend! Use ice, at least once a day, to help the swelling resolve. And, don't do anything that hurts or leaves the knee feeling much more sore and/or swollen afterwards. If the swelling does not go away soon, go back to the doctor.

kavahni

Just curious if the doc mentioned ITB to you. Outside knee pain is usually that-though swelling is not associated.
Be sure that you stretch religiously after you work out. Here's a link to a four minute leg stretching routine that can save your legs/knees. I speak from experience!
https://m.youtube.com/watch?v=P0Sg1MHhmjY