Chances are the problem lies somewhere in the midst of you not knowing exactly how much CO2 there is, and having not dosed at all. You definitely should begin a regular fert routine, and you should crank up the CO2 as well. At least until you get your crop checker. You don't have any fish in the tank, right? So no worries about killing any fish. But 1-1.5 bps is a pretty low rate for a 55g.
Also you should tell us what kind of filtration you have. For all we know, you're using a nanofilter or something.
It's very possible the plants are just getting used to the tank. Some pictures would be helpful, I suppose.