I have had enlarged tonsils for three months and can't get rid of this mucous in my throat, what could it be?

Large tonsils. It could just be your enlarged tonsils, which tend to pool secretions (provide a lot of nooks and crevices). That they are enlarged is indicative that there is already chronic inflammation present. Once these get significantly enlarged they take a long time (several months) to go down. If they don't go down after several months, and they are still bothering you, you might consider tonsillectomy.