Weird pain symptoms. I'm kinda confused.

I get this very agonizing pain in my knee, but not when I do intense cardio. I can burn up to 600-800 calories in like a HIIT step class, spin class, badminton for 1 hour, burn like 350-400 calories in like 30 minutes for badminton. I can run around and I won't feel much pain when I'm running side to side or doing any... I don't know, it's just my pre-assumption. But when I get up in the morning and I walk to the bus stop, which is like a 4-minute walk from my house, I get this agonizing pain in my knee from my calf. It's sort of like a shock and I don't know what it is. But it doesn't hurt when I'm doing intense cardio. But it hurts when I'm walking, pace walking, or even running. I don't know. I don't understand this. I'm kinda confused.