cat phobia?

[novee]

hey all
ive had cats as pets all my life but never xperienced anything like this
my male cat almost 2 yrs old wasnt usually so interactive with humans but now he has developed some unusual phobia of open spaces, as far as i can tell, he doesnt like going out of the house any more (which is absolutely opposite to the way he was before):sad:
Infact he looks for corners, bed n tables he can hide under, he only comes out for food n looks ok otherwise except for feeling hot to the touch..... this has been goin on for 3 weeks now....my vet gave him antibiotic injections to take care of any possible infections but he isnt any help either....(we dont have proper qualified vets where im at)
im really worried now n hoping someone can help me out.....