Go see the doc so you can find out what it's all about. It's probably something minor like a major growing pain, but it will take a doctor to figure thjat out and give you a strategy to best manage the pain and prevent future problems.
How old are you? First thing is talk to your parents about a dr. visit like ^^^^ said. You need those knee's for a long time! Get it checked now before you really get hurt. A little soreness is one thing, collapsing is different.
i understand. that is why everyone is telling you to get to a Doctor. there are a lot of things that can go wrong with the knee. you could be walking around with a partially dislocated kneecap and not know it. so, tell your mum and get to the Doc.
Dear child you have just told the whole internet about this issue, you really do need to tell your parents.
Frankly small pains grow into big pains, pains that mean little can turn into life long problems. Believe me when I tell you to tell your parents and see a doctor. The sooner it is looked at the sooner you will not be in pain and enjoying gym.
I don't know why you wouldn't want to tell your parents. Your parents care deeply for you and want only the best for you. If your injured they should know so you can get the medical help you NEED! It's better to get these things looked at when they are minor and can have an easy fix than waiting until its serious and your laid up for months trying to recover.
Put your Big Girl Pants on and tell your parents what is going on TODAY.
How old are you? if you are a teen then its time to grow up and do what you know must be done.
Tell your parents! My son at 15 had knee surgery was off his leg for 6 weeks(no weight at all). This surgery saved his hockey career! As I tell my kids "man up and do the right thing!". Get it checked out by a doctor ASAP before it can't be fixed.
Honestly if it were my DD I would hope she would come right to me long before she thought to post something on the internet. If she didn't I would be really worried that she didn't feel comfortable enough to come to me with any issues.
The ONLY ones that can really help you is a DR and your Parents.