Hurt knee doing lunges? Help!

Twinsmama75

I have been doing 30DS and I think my form was poor on the lunges and my knee went past my foot (I have zero strength in my core) and I guess I injured my knee b/c I cannot do jumping jacks, jump rope, or side lunges anymore. I feel pain when I walk up the stairs, but it's not horrible or anything.

I keep taking a few days off of exercising for it to "heal" but I still can't do any jumping or lunges. I am frustrated b/c I was doing good for the first time in my life sticking to a workout regiment and now I don't even break a sweat doing it b/c I can't do any of the cardio.

Advice? Go back to the ellipitical and forget Jillian for a while?