Big blisters sore and swollen after 3 weeks after lip fillers with juverderm .

Hello missyminx,Based on the picture you appear to have a herpes outbreak (also known as cold sores).  This can occur anytime after trauma to the area around the lips whether it was a filler such as Juvederm, Botox, or chemical peels.  They can also develop with stress.  Avoid rupturing the blisters as this can lead to a different type of infection.  There are pills and topical creams you can receive to help the outbreak go away faster but this can be discussed with your medical provider.  In the future, you may consider requesting an antiviral pill before receiving any treatment around the lips to help minimize the risk of this occurring (but it won't make that risk zero).  I hope this helps and good luck.  

This could be herpes simplex(cold sores, fever blisters). These can have multiple triggers. Sun exposure is a very common trigger. While injury can also do it, it would be unlikely 3 weeks after Juvederm injection. Anti-virals like valcyclovir can be used to treat this. If it recurs frequently, valcyclovir can be used to help prevent such recurrences.             jlr