Females are more likely to have "relapses" in their potty training. With doxies (and other small dogs), they often don't like squatting in damp grass or on cold dirt.
The main thing, though I know it's the hardest, is that you can't bring them back inside until they do their business - all of it. Remember, it takes a bit of time after eating until you get a bowel movement, so you have to give them time to get things moving inside. It could take 10 minutes. I've been out for 2 hours before with a puppy.
With taking them out every two hours, they aren't going to poop each and every time. At 7 months, you might try reducing the trips out to every 4-6 hours.
Also, take note of the times of day when they are pooping (whether inside or outside). Use that as your guide for when they need to go outside for potty time. Digestion times differ in dogs, so you want to determine how long after eating your dog's bladder and bowel need to be released. As they can sleep through the night, you know they can "hold it" for 8 hours. Look at when you feed them last, when their last successful potty time was (on both counts either inside or outside), and how long between those successful potty times were. Use that as your guideline for outdoor trips.