Hi.. Welcome to HEALTHCARE MAGIC.. I have gone through your query and can understand your concern.... As per your complain as you are regaining the sensations in the area which got numb due to nerve damage it means that the nerve injury is being healed and the chances of relapse of nerve damage without any trauma are negligible.. As you have got mild numbness it can be as a result of inflammation caused inside the lower lip by the sore or ulcer.. As you are catching cold along with a sore in mouth it is more of a chance that you have a cold sore caused by herpes simplex virus but any final diagnosis can be given after visual inspection of the ulcer and any laboratory investigations if needed and for this you need to consult an Oral Physician.. There is some level of tingling,burning or numbness can be felt when there is occurrence of the cold sores and will subside gradually as the sore will resolve.. If herpes is diagnosed the doctor will advise you to take oral antiviral therapy like Acyclovir, Valacyclovir,Famicyclovir etc.. Topical application of antiviral ointments over the sore is also advised.. In case if it is not viral infection then it is a canker sore and doing warm saline gargles, soda bi carb gargles and application of a numbing agent with a steroid like Kenalog in Orabase 0.1% and taking a multivitamin pill daily for 15 days will relieve.. Hope this information helps.. If you find the answer helpful please give me a Five Star Review and click on found the answer helpful as a token of appreciation.. Thanks and regards.. Dr.Honey Nandwani Arora..