I'm just stepping in until an expert comes along, but the first thing I'd wonder is how often you're doing water changes?
I'd always done fish-in cycling, although I now use a different method, but I always did LOTS of water changes, starting with daily, because fish not only poop but respire ammonia, and a very low level of ammonia/nitrite is still toxic and can stress/sicken/kill fish.
I've heard some of the weirdest advice from various LFS's, and in fact was just recently helping a friend of my brothers who'd had disastrous advice - even though she was WORKING at a chain pet store.
People advising usually like to see info like tank size, water stats, type of test used (as some are fairly inaccurate, especially if older) temp, water change routine, tank cleaning procedure, etc., so if you have this posted, it would be helpful to the experts which will be along shortly.
What's happening in your tank (NOT EXPERT) is that you're part-way through a cycle, and the ammonia's being converted by one type of bacteria into (toxic) nitrite, but another lot, which will convert the nitrite into nitrates hasn't yet populated the tank.
These bacteria types will propagate throughout the tank, gravel, driftwood, ect., so you don't want to overclean these, just change enough water to reduce the toxins.
I'm guessing you were not able to obtain cultured media for your filter from an established tank in order to rapid-cycle.
The bacteria in your filter has the water and 'nutrients' on which beneficial bacteria will feed circulating through it and it is essential that this media NOT be changed regularly or in full, as many LFS' will advise, or be rinsed in tap water, which will kill the bacteria on which your fish's lives depend.
At least, they will once it's built up, but it generally takes about 6 weeks and sometimes more to establish the required bacteria to support however many critters are currently in your tank.
If I were you, and I had nitrite in any of my tanks, I'd be doing a large water change right now, and if you have records of your water stats (run a test prior to doing the water change, if you haven't done one today, so you know what your fish have been subjected to) and as soon as that's done, if you can post the required information, you'll have all kinds of experienced help.
But I would NOT leave the fish in any level of nitrites any longer than is humanly possible - even if you don't see any obvious signs, the fish are being silently poisoned.
Thank you so much for being smart enough to look for information, and to come here, where so many experienced fish keepers are so happy to help out.
And it's a very great pleasure to make your acquaintance - somebody, soon will be far more helpful than I can be.
don't get my started on trying to alter PH!
