Something wrong with my body?

I am a 5'2" 115lbs 18 year old girl and my knees have stretch marks and they get stiff. Why do my knees have stretch marks on them? Would losing weight help me knees not get stiff? Also my feet and hands get stiff too. Do I have arthritis? LIke whenever I pick weeds or pick up a toddler my knees they get tight and stiff. Like its sometimes uncomfortable but its not unbearable. Also my joints crack. My knees crack whenever I go up and down the stairs. My fingers need to be cracked because they get stiff if they don't and a couple of my nuckles are bigger than the others because they are the ones that I crack the most. Is there something wrong with me?