Very Puffy Snail?

[mariearound]

My Cornu aspersum (also called Helix aspersa, but usually just common garden snail) is very puffy! He has been this way for a month! I have read other threads where people have had the same issue and I don't mean to post unnecessarily, but he looks way puffier than other pictures I have seen so I am worried. 
I vary his diet and he lives alone so he isn't mating, so I know those aren't the causes. I also give him temperate baths (which he loves). Here are pictures:

drive.google.com/open?id=0B_yA5ejzVtpMT0pncTJrLUkxNkU

It recedes mostly when he moves around. I have thought of some possible causes: maybe I  am not exercising him enough? Or the humidity in his tank is too high? (I keep it between 75% and 80%)
I wash his food but maybe I am not washing it well enough?
He is behaving normally enough minus the weird faces.
Thanks for any help guys! <3

[diegothesnailkeeper]

In the third picture whats that thing on his shell? its the greyish purple thing on his shell that I'm talking about 

[mariearound]

Feb 6, 2017 22:27:19 GMT diegothesnailkeeper said:

In the third picture whats that thing on his shell? its the greyish purple thing on his shell that I'm talking about 

That is just a friendly slug! I pulled him off and put him in his proper tank after this impromptu photo shoot.

[mariearound]

Just a quick update: I have been handling and bathing him, exercising him more, ect and he seems to really enjoy it! I have noticed a few things:
He has some abnormal shell growth, parts where it is discolored and looks warped , however these are minor. He also has a small dent on his shell where it almost looks like he was poked too hard with a pencil (obviously this could not actually be the case and is just an example). I do not know whether these shell issues occurred in captivity or not but he was already very large when I found him on a transport truck a year ago. As far as I know he has not sustained any injuries in captivity but he has continued growing.
Anyway, could these shell problems be causing swelling of the inside of is shell? (That part under the lip?) Is there anything I can do to soothe this? Thanks in advance!