I could advice to post a picture of the leaves, even if it doesn't have its urns, sometime that might help ID the plant. Where did you bought the plants, was it at Lowes, Home Depot, or from a nursery.

But one mistake I read is that it gets limited light. It suppose to recieve bright filtered light for at minimum of 8 hours. If its in the shade most of the time, that's one reason it nevers develop its urns.

That's why the plants sold @ Lowes and Home Depot are stringy and dying from lack of light. They keep them in the shade.

To my experience I don't recommend cutting them becuase when I did that to my 1st nep when it was growing weakly, I killed it.

For now, I recommend increasing the light by putting your indoor greenhouse next to a window that receives many hours of sunlight... if it's possible. But you have to check that it doesn't overheat you greenhouse by opening any vents if it has any.

Generally speaking, Neps need a good 12 hours of light per day, since they are essentially equatorial. I would recommend fluorescent light over it.

How deep is your growing vessel? A plant that old probably needs some room to expand its roots.

What media are you using? Neps do best in what is referred to as an "airly mix" and many use a combination of Perlite and orchid bark, along with peat, sand, LFS,..

What temperature is it in. Depending upon the species, it may be too cold for it.

If you get us a picture, maybe we can determine what you have. If it came from Home Depot or Lowes, it is likely to be an N. ventrata, which is a pretty tolerant cultivar.

Yeah, I also would advise repotting the plant in new mix, I find coconut husk, peat, and orchid bark in 1/1/1 mix to be good, and get it into a larger pot if needed. Make sure that it gets plenty of drainage and no water tray under the pot to reduce the chance of root rot. They like their soil moist, but never too wet.

More light, as Hunterkiller advised, and possibly a light foliar feed of orchid fertilizer in a 1/4 or less dilution might perk the plant up. Once it starts making pitchers again, stop fertilizing if you decide to try it... I never fertilize mine. My Nepenthes do best under 12000 lumens of florescent light for 16 hours a day all year long. I have them in a south facing window with a single 100 watt florescent compact on then and they are doing O. K. for now. I expect them to do better once spring photoperiod fully arrives.