A new tank has not had the time to build up the proper beneficial bacteria needed to break down fish waste and keep all your parameters in check. Many times you will see an ammonia spike with a new tank which is not healthy for your fish and can cause them to stress. It would be a good idea to get yourself a nice freshwater test kit. Most of the times when your fish are acting strange, a simple water test will reveal why. Most of the times it usually high ammonia or nitrates or sometimes a PH fluctuation. If a kit is too expensive check with some of your local fish stores, some will test your water for free.