You discovered the downfall of potty pads. For tiny dogs, maybe these are somewhat helpful. But to most dogs, this actually teaches them to potty in their living environment. And to have a fully housetrained dog, you have to train them twice - on the pads and then off the pads to outside. It's really best to skip the pads unless you just can't take them out because you aren't there to do so.
I would suggest always taking him out on leash and going to a specific spot every time. Remind "go potty" and wait. and wait. And when he finally does his biz, then have a heck of a pee-pee party! Lots of high voiced praises, a treat, pet on the head and then a little play session. Going potty should be the most exciting thing imaginable!
Taking him on leash makes sure of several things:
1. He can't go or do anything until he potties.
2. You can check to make sure he is fully emptying his bladder.
3. Can't praise if you aren't there to see it happen
4. You can check stools for any irregularities
5. Eventually he will learn going out on leash to that particular spot to go potty and get lots of happy praise! He will automatically go and do his biz upon command.
The most common indicators of a needed potty break is, after naps/sleep, after meals, after a drink session, after a play session, really any time fluid goes in or excitement goes up. Each time praising the heck out of him.
If accidents happen in the house, do not punish the pup. This will only confuse him, especially since he was taught to potty in the house. If you catch him in the process, give an "ah-ah" sharply and immediately take him out to finish. If you find a puddle after the fact, clean it thoroughly and with an enzymatic cleaner to void any residual stain that may entice him to go there again. Chalk that puddle up to you being lax in getting him out at an appropriate potty break.
Sticking to a schedule will help tremendously. A feeding schedule. Sleep schedule. Play schedule. etc. This way you will be able to log and predict his potty patterns and can adjust your schedule to them to help with training.