Sore throat from 2 months. Suggest.

I have a sore throat or what would I say it  redness and in  back part of throat with little bit pain while swallow . I consulted the doctor and had a throat culture which turns to be negative , then I went to a ENT specialist and he adviced calithromycin or cliff tablet ,one gastic tablet and a pain killer but with no luck, then I went to RML hospital and there doctor advised me amoxicillin for 6 days and sefixime for 5 days but result was the same no effect at all. It's been 2 months I have this sore throat . Please suggest what problem could it be and please let me know what tests need to performed. Moreover, I posted a query earlier here as well and one of the doctor suggested me it seems to be post nasal drip and adviced me anti- allergy tab and steroid nasal spray. So can anybody suggest me the name of any nasal spray and anti-allergy tab for the same. Please suggest.