It could be many things. It would be very helpful if we knew if it was central air or a window unit and how old it is.
Just a couple of suggestions. The charge may be incorrect. If a home unit fixing this is a professional's job, it takes special equipment and training; and if low it also means there is a leak to fix first. If it is a window unit, it is either under warrantee or you junk it.
Restricted (dirty) condensers or evaporators are generally not too expensive to fix, and then there is the question of the fan and distribution system for a central unit.
There are others.
How old is it? When was the last time it was serviced (cleaned)?
If a window unit do you have the fresh air switched on or recirculate?