Soreness and hardening 6 months after injections, is this an infection?

It sounds like it could be a viral infection or possibly a reaction to a medication you are taking. It is unlikely that the swelling you are experiencing is related to the filler treatment you had six months ago. I recommend you consult with a board-certified dermatologist for evaluation. Best, Dr. Emer

Usually six months after the fillers, infection is rare. Also this far out the filler should be all settled. This could be an additional event like cold sore or viral infection but the best way to determine would be by a physical examination. 

Have you had any sort of viral infection the last few weeks?a cold sore coming on?  or any trauma to the lips. I would go back to your provider to take a look at your lips. 

Thanks for the question. Generally, it is unlikely to have symptoms of lips soreness 6 months after lip filler treatment. You may have a local inflammation, minor trauma, possible allergic reaction to a medication or a viral infection causing a cold sore. This should last no more than few days. In case your symptoms do not resolve, I would recommend you to see your doctor for a detailed personalized evaluation to find out the reason for your symptoms.I hope this helps.

It is unlikely that your symptoms are related to your filler treatment.  It may be a sign of a viral infection, such as a cold sore.  If your symptoms persist I would visit with your primary care physician.

6 months is a very long time and one would not expect infection that is related to filler. However, there is a possibility of granuloma formation that may need to be treated. You should definitely see your injector for evaluation.