Why is my mini doing this?

by Cassandra
(Bountiful, UT, USA)

I have a 4 year old mini. We live in an apartment and he has been living with us for 2 years now.
He was great for about 7 months and then started going to the bathroom on the carpet even after he had gone outside and gone to the bathroom. Because he wouldn't stop we wound up having to crate him while we are gone. He has been crated for the last 6 months (only when we are gone for work, school, etc.) and has not had any problems.
In the last 4 days he has been going to the bathroom in his crate every time he is left in it. He is being taken out to go to the bathroom multiple times before being put in his crate for the night but seems to just keep going to the bathroom.
Any ideas on what might be going on with him?