Why is sex with my boyfriend so painful?

I (23f) have been with my boyfriend (M26) for a few months now. At first the sex was great, but after about a month of being together it started to become excruciatingly painful. After the tip enters, it’s nothing but a sharp painful stinging and burning. It’s getting worse while time goes on. I tried to talk to my OB about it who suggested we switch lube and start in different positions but nothing has worked. We tried extra foreplay as well but nothing. This past attempt made me scream in pain. It’s gotten to the point where we can’t have sex at all. I feel like drs aren’t taking me seriously and I’m officially at a loss. Has anyone else had this happen? What could be causing this? ((We also have both been tested- negative for everything))