I have a mini pin.. he is already a year old.. had him since he was
Two weeks old.. I potty trained him with out no problem
He can go at least 8 hours with out doing inside my house
While I am out.. all of a sudden for like the past 5 days he
Has been doing it inside, an worth is that he does it right in front
Of me an the door being opened in the back yard!
What's going on.. can someone help me..

Take him to the Vet - it very well could be a bladder or kidney infection or something along those lines.

ANY change in behavior is a concern and the dog should see a Vet.

Small breeds are notoriously hard to potty train.
Unfortunately I am not familiar with Min Pins as I do not know anyone with the breed personally.

Like Judy said a vet check is your number one port of call to rule out urinary infections, once he has had the all clear at the vets we can work on behavioural problems.