Hi qejm0g. Know that you are not alone in struggling to figure out what exactly a seronegative diagnosis means and even ending up questioning yourself and the diagnosis. Our contributor Monica wrote about her experience with these questions here: https://rheumatoidarthritis.net/living/ra-or-not-ra/.
The main thing is to know what you are feeling be willing to advocate on behalf of yourself. It is estimated that about 30% of those with RA are seronegative. There is a reason the diagnostic process is supposed to entail a lot more than the blood tests (see https://rheumatoidarthritis.net/diagnosis/).
My wife, Kelly Mack (a contributor here), was diagnosed at two years old with a very aggressive case of juvenile RA, has had RA for 40 years, and used a wheelchair since her late teens. At the time of the diagnosis they didn't even do rheumatoid factor testing. Last year, just out of curiosity, her rheumatologist ran an RF test and it came back negative. Blood tests truly don't tell the entire story. Wishing you the best. Richard (RheumatoidArthritis.net Team)