You didn't state when in December you brewed the lager, but just taking the days until 2 weeks ago, you have had it sitting in your fermenter for at least 9 weeks. At 40F, the yeast cells would have slowly prepped themselves for preservation after the available sugars and byproducts produced by the yeast and settled to the bottom. If you did not stir up a bit of yeast when you siphoned/drained your wort into your bottling bucket or add yeast specifically for refermentation, you may be a bit short on available yeast cells to cause rapid carbonation of the lager. At what temperature have the bottles been kept while carbonating? How much yeast did you pitch into what batch size?
So in trying to recover, I would suggest the following options:
(1) if the bottles have been stored at 40F or cooler temperatures, bring the bottles up to room temperature to carbonate,
(2) you can take some dry yeast and sterile water, proof the yeast in the water and then uncap and add a ml or so of yeast solution to the bottles and cap immediately,
(3) Chalk the whole thing up to experience gained and start over again.