Hi there,
I started a thread about much the same thing a little while ago and got some help. My problem is that my 10 month old has suddenly decided to miss the pee pads for anything other than a little piddle. She had a weird "relapse" kind of thing after reliably using the pee pads for months. Of course, her relapse started after she was spayed. It has gotten better recently.
The advice I was given was to keep on her about it. When she starts to go, make sure she's on the pad -- I'll pick her up "midstream or mid-other" -- and then give her extreme praise as well as a treat for going in the right place. If she goes elsewhere and you catch her, giver her a stern "NO:" but don't use her name, just the no. (Want her name to be associated with good things all the time.) and withhold attention for awhile. It doesn't have to be very long (and with faces like little sweet Yorkies have, how could anyone ignore them for very long?!) That stuff has been working very well for the kind lady who answered me. She uses little bits of cheese (processed is less likely to cause binding) for rewards. I've been using Pure Bites freeze-dried chicken and/or beef liver.
My girl gets excited for the reward and I really ham it up. This morning, there was "evidence" that she'd used the pee pad despite me being out to pick up my brother from the airport, so she may be on the way back to using it "full time" again.
Hope that helps a bit. I understand how you feel. If you can believe it, my little girl was reliably using the pee pads more than 98% of the time when she first came home at 8 weeks old; I'd seen her using it at one month old during the pre-adoption visits. I was stunned when she just suddenly started having accidents.