Hi.. Can understand your concern.. As per your complain the painful ulcers all over the mouth can be CANKER SORES or APTHOUS ULCERS. There are a number of reasons considered as predisposing factors for the occurrence of canker sores but the exact cause is still unknown.. In case if you have severe pain in the ulcers you can take anti-inflammatory painkiller like Ibuprofen for relief.. Gargles using 1:1 solution of milk of magnesia and benadryl liquid can be helpful.. Gargle with dilute hydrogen peroxide can be helpful. You can apply milk of magnesia on the ulcers after the gargles. To avoid pain and discomfort while taking meals you can apply numbing gels containing Lignocaine or choline salicylate . In case of large painful sores which does not get relieved by these treatments then steroid tablets has to be taken.. You can also apply steroid based ointments on the sores to reduce redness and irritation caused due to inflammation.. Sucking on ice pops can help.. Drink plenty of cool water and other cool liquids for relief as well as avoid dehydration which can cause dryness in mouth and irritation caused due to dryness.. Avoid hot,spicy and sour food items as well as hard foods. Take soft and cool diet.. Hope your query is solved.. 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.