I Have Been Having Knee Pain In The Right Knee

I have been having knee pain in the right knee and some days are worse than others. The other day I realized I had a lump on the outter edge of my right knee probably about the size of a golf ball. At the time it wasn't hard to touch cause u could press on it and it kinda felt squishy but now it feels harder than it was. I was wondering if it is just fluid build up or could it be more??