Side pain

For about a month and a half now I've had this pain on my right side, it feels like a bruise but worse. The pain isn't constantly there, I only feel it sometimes when I lay down. It's strange because the pain will be there one second and then it's gone. It's definitely gotten better since when I first had it, but my doctor isn't too sure what it could be. I'm only 17 and I play soccer, so I don't remember if I was ever hit there or not but I have no clue as to what it could be. If this has happened to anyone before, it would be very helpful if you could help. Thanks!

[Caryopteris]

Have an abdominal ultrasound.  If that's okay, consider trying Metamucil.  You can take the capsules if you don't want to mix the powder with water, but you still have to drink water.