What is this knot on my rib?

I started having alot of pain on my right side around December it came and went. Then in March it started hurting again it was waking me up at night hurting all night. I went to the doctor and she said it was probably a pulled muscle said to take ibuprofen and gave me a muscle relaxer and steroids for a week. I started feeling around and I have a small pea size knot on the rib on my right side. The pain was off and on then in April I saw another doctor said the same thing said they wanted me to have an MRI...but I have no insurance. I don't really feel bad but over the past 3 years I've gained 30 lbs I wonder if that may have something to do with it. Has anyone else had this problem? It doesn't hurt all the time it didn't hurt for a couple months then last week it started hurting again and hurts constant no matter how much tylenol or ibuprofen I take. I'm kind of scared but can't afford the test because I have no insurance. What could this be?