The lumps could indeed be a symptom of your RA, but they could also be something else. It's really important when you have a chronic illness to find a good doctor you trust and can contact when you have concerns. Early diagnosis and symptom relief can make a huge difference when it comes to staying active and feeling well.
A common tendency with RA and other autoimmune diseases is to attribute every symptom to the disease. I agree that the best course is to check with your doctor and let him/her have a look.
All the best to you!