Contact lenses Problems! Pleas help : ASAP?

Ok say basically i went to spec-savers On monday , and they said that i couldn't were contacts for a month because under neath my eyes they are swollen .. because i wore my contact lenses for too long , well that's what they said , [ i wore them for 12 hours instead of 9 ] is this what has caused the swelling? or is it an allergic reaction ? and also there going to put me on trial contacts , So is there a possibility i wont be able to wear contacts again?