A month in secondary isn't really long enough to need to have added more yeast.
What temp are you storing them at?
The
3 weeks at 70 degrees, that we recommend is the
minimum time it takes for average gravity beers to carbonate and condition. Higher grav beers take longer.
Stouts and porters have taken me between 6 and 8 weeks to carb up..
I have a 1.090 Belgian strong that took three months to carb up.
Temp and gravity are the two factors that contribute to the time it takes to carb beer. But if a beer's not ready yet, or seems low carbed, and you added the right amount of sugar to it, then it's not stalled,
it's just not time yet.
Everything you need to know about carbing and conditioning, can be found here
Of Patience and Bottle Conditioning. With emphasis on the word,
"patience." 
If a beer isn't carbed by "x number of weeks" you just have to give them more time. If you added your sugar, then the beer will carb up eventually, it's really a foolroof process. All beers will carb up eventually. A lot of new brewers think they have to "troubleshoot" a bottling issue, when there really is none, the beer knows how to carb itself. In fact if you run beersmiths carbing calculator, some lower grav beers don't even require additional sugar to reach their minimum level of carbonation. Just time.
I've carbed hundreds of gallons of beer, and never had a beer that wasn't carbed, or under carbed or anything of the sort (Except for a batch where I accidently mixed up lactose or Maltodextrine for priming sugar). Some took awhile, (as I said up to six months) but they ALL eventually carbed.
There would be no need to toss the beer even if it didn't carb up (which it will), you could always add more yeast. rehydrate said yeast in water (or use liquid) in a sanitized container, get a children's medicine dropper with ML gradients like this,
Sanitize it, open beer bottle, suck up slurry into sanitized eyedropper, squirt 1 ml of yeast into bottle, then re-cap. Give the bottles a shake, and then walk away for another 2-3 weeks to give that yeast a chance to do the job.
I wouldn't do it for at least another month though.
But I doubt you'll need to.
No go rinse your mind out with soap for even THINKING about tossing a batch of beer.
