Hi.. Thanks for the query.. Cold sores occurs in the form of clusters of fluid filled blisters and not just a swollen lip.. Swollen lip can be an indication of allergic reaction, and not always cold sores.. So for confirmation before you apply anything or take any medication, you should consult an Emergency room or a Physician and get evaluated and a blood test can be done for checking allergic reaction as well as Herpes virus infection.. For now you can take antihistamine like benadryl to reduce swelling and also do cool compresses over the lip.. If viral infection is ruled out antiviral medication like Acyclovir and Valacyclovir can be advised.. Hope this helps.. Regards..