Please help me my knee swollen

Hello guys so my knees where swollen yesterday, Yesterday I ran to work for 2-3 minute or less then power walked the whole time when I got to home my knees where swollen and hurt when I tried to bent them but after I slept today there is no pain and 90% of the swelling went away its not the first time it happened to me again at grappling practices but this is the first time that two of them happened back then only one swelled up in my grappling practice please help me what could it be arthritis? But I’m only 18😞😞😞