Car wreck question - injury related

I was rear ended 10 days ago at a red light. Other guy was driving a truck and I was in my son’s car and there’s not too much damage but I’m actually hurting in my back and neck now. I didn’t go to the hospital because I wasn’t hurt at the time but around day 4 I was really beginning to feel pain in my back and neck. No numbness or tingling - just hurting. Should I still be this sore? Guy was probably only going about 20-25mph when he hit me.

How does this work? Do I just go to the doctor and tell them what’s going on? I don’t want to be one of those people who claim everything under the sun after wrecks but I really don’t want to be responsible for the medical bills if I go get checked out and there’s something wrong. Im also worried that once I open that can of worms with the insurance company they’re gonna be assholes and make me get an attorney. I don’t want to go down that road.

How do I go about this with the insurance company? How do I walk this fine line?