Back of Freezer Swelling with Some Frost

Freezer hasn't been working properly. Some items closest to the back of the freezer were frozen but things closest to the door have not been. The door would get stuck after being closed every time. Just noticed on Friday that the back of the freezer is swollen and a bit of the bottom of the freezer is as well. Turned off the refrigerator, unplugged it and defrosted it for the past 2 days. The backing/bottom of the freezer is still slightly swollen, the visible frost is gone but there still seems to be some coolness coming from the back. Should I assume it's "defrosted" and turn the refrigerator back on? Any idea what the cause is? It wasn't over filled but maybe we had some items too close to the vents?