Hurts when I bend my knees, when i get up or sit down for example. This was after my kickboxing session?

When I'm sitting or standing I don't feel anything, but when I get up or sit down and thereby apply pressure to my knees it hurts like a mother. Two days ago, I tried kickboxing for the first time, but it only started hurting yesterday. Is this just normal? I never had this before. Not this bad anyway.