hi and welcome ,
As you have mentioned you are suffering from flu with symptoms of sore throat
,body ache and fever it is common to get the oral symptoms of cold sores ,gum and lip swelling
Oral symptoms like gum swelling called gingivitis and lip swelling , cold sores are caused may be due to deficiency of vitamin B especially Vitamin B12
and vitamin C .
It can be related to stress or low immunity induced oral symptoms.
i would suggest you to start with Multivitamin
supplements and vitamin C lozenges for 5 to 7 days along with a course of antibiotic and anticold medicines for treatment of flu.
Use lukewarm saline water or antiseptic mouthwash like betadine or chlorhexidine
for oral rinsing.
drink lot of water and keep yourself hydrated.
i hope this helps,