Hi.. Can understand your concern.. As per your complain first of all I would like to tell you as a DENTIST that although you are fearful of going to the dentist as you are hesitating about the question that why you have retainer not removed or about poor oral conditions,Just RELAX.. A dentist can understand your fear and will treat you with all compassion and keeping in mind your concern.. So better don t hesitate,just move ahead and get yourself in a better oral health.. Now moving to your problems.. The swelling and soreness of gums as a result of inflammation is due to infection in the gums due to poor oral hygiene.. The broken wisdom tooth from which black particles are removed shows that it was decayed and there must be still some root pieces remaining in the jawbone and you should get it extracted as it can get infected and cause you pain and swelling any time it become active.. The retainer placed will cause food accumulation and infection in that area and further infect the gums as well as decay the tooth as well as will get foul smell in mouth due to food lodgement.. The infection in gums can be very well relieved by getting a professional cleaning done followed by application of topical antibiotic ointments that has to be massaged over the gums for stimulating the gum growth and reduce infection.. Oral antibiotics can also help.. For sensitivity you can apply desensitizing toothpastes over teeth.. Learn proper brushing technique from your dentist.. brush twice daily once in morning and once during bed time and use antimicrobial mouthrinses to gargle.. Hope this information helps.. If you find the answer helpful please write a positive review and click on find this answer helpful as a token of appreciation.. Thanks and regards.. Dr.Honey Nandwani Arora.