What Causes Popping Sound In The Knee With A Lump?

I am 28 years old and I have always had knee issues since I was about 10 when I wrecked my bicycle into a pile of pebbles. My Mom never took me to the doctor and I think I have always had a problem with my knee more than I should. Ever since then I can make my knee pop really loud and more recently in the last year and more even recently I have started to notice a lump to the side of my knee cap. It mainly only hurts when I am on my knees and the pain is so unbearable that I nearly fall over. And more just in the last 4 days it has gotten worse. Rhumatory arthritus is in our family, don't know if that could be anything. Now even if I just slightly touch my knee with my hand it hurts and is about 75% larger than it was 5 days ago. I am also pretty over weight. (300Ibs 5'6"-Female) Can you tell me if it's something that sounds super serious or not. And if I should take this serious and get it checked out soon?

Thanks