Severe Knee Pain

As the title suggests, my problem I faced during my leg session earlier was almost unbearable joint pain in my knees.

I warmed up with light leg extensions, and almost immediately it became to painful to carry on; although when squatting I experienced no discomfort at all. This was also evident when using the hack squat, I could go nowhere near parallel without it feeling like my tendons where being torn from my knee; yet when leg pressing I felt no discomfort at all.

I take regular Omega-3 capsules to try and counter this problem - one of which I faced when I first started lifting. What supplements or dietary additions can I make to relieve myself from this problem, as I feel it will seriously affecting my exercise selection regarding leg training in the future.

Thank-you in advance for any advice, Tom.