Hi.. Welcome to HEALTHCARE MAGIC.. I have gone through your query and can understand your concerns.. As per your query a small round lump under the jaw seems to be probably due to swelling in the lymph node leading to Submandibular lymphadenopathy.. As you recently had cold and sore throat, therefore lymph node enlargement is secondary to infection only.. Many a times swelling in lymph nodes reduces gradually after the infection subsides, so you need not to worry about it as the swelling will subside soon.. You can however do alternate warm and cool compresses over it and also take anti-inflammatory painkillers like Ibuprofen.. Secondly pain in apthous ulcer is a common finding and for this you can start applying numbing gel containing Lignocaine over it.. You should start taking a Vitamin B complex tablet daily for a week.. You can make a solution of soda bicarb in water and gargle with it.. Do warm saline gargles.. You can also suck ice pops to reduce inflammation and pain.. You should avoid hard, spicy foods.. Hope this helps.. Regards...