After you have had an ear infection
, the fluid can stay around for 3 months or longer. In about 50% of people, it is gone in 1 month, in 90% it is gone in 3 months.
If the pain is intense, it may be that the infection is not fully cleared. If it is pain associated with popping and crackling in the ears, but is otherwise not there, then it may just be left over fluid that is not infected.