Haier freezer not defrosting and freezing up

Our Haier refrigerator is not working properly. A week ago we discovered freezer was way too warm and food thawing out and upon closer investigation the whole freezer unit was frozen - electrical, coils, everything. We spent the night thawing it out and for a few days it was working so well [maybe too well - freezing our drinking water on the next to lowest setting in fridge]. As the week went on we saw our ice cream getting soft, while the rest of items still frozen solid. Changing the temp to colder did not improve the freezer situation. Just went in there and found the back of the freezer full of frost on back wall. Husband and I are not that appliance savvy - any ideas of what may be causing the unit to keep freezing up? Owners manual lends no helpful information.