Hi.. Welcome to HEALTHCARE MAGIC.. I have gone through your query and can understand your concerns.. As per your complain soreness in mouth along with metallic taste and dryness in mouth are all inter-related factors.. Redness and pain in mouth on eating spicy or citrus foods is pointing towards APTHOUS STOMATITIS and if you have a dry mouth it can be a very potent cause for inflammation inside mouth as it can cause thinning of mucosa along with inflammation and ulceration also.. Other causes can be Nutritional Deficiency [Iron, Vitamin B12 and Folic acid] , hormonal changes, acid reflux, tongue trauma due to some sharp teeth or tongue biting habit, excessive intake of sour and citrus foods, uncontrolled diabetes and other immunocompromised conditions etc.. You need to consult an Oral Physician or a general dentist in this regard to get evaluated and treated.. If there is dry mouth then Altered taste is due to reduced saliva flow only as the saliva maintains taste buds and in the absence of appropriate quantities of saliva there is alteration in the function of taste buds leading to altered taste.. For apthous stomatitis you can do warm saline gargles Gargles with 1:1 solution of benadryl and milk of magnesia can help.. Apply numbing gel over the sore for relief from pain especially during eating.. Take Vitamin B complex tablet for a period of 15 days.. Avoid spicy, sour and acidic foods.. To alleviate dry mouth chew sugar free chewing gums and instil artificial saliva drops containing Methylcellulose.. Use specialised mouthwash like Biotene.. Hope this information helps.. Thanks and regards.. Dr.Honey Nandwani Arora.