I have to agree that your tank sounds over stocked.....especially now hearing about the frogs. A 10 gallon tank can support 10" of adult fish.....Since the recommendation for guppies is 3 females to one male (cuts down on pestering), your tank could support one such group, and that is all....Even the fry would have to be removed to a different tank, to keep from overcrowding. Guppies are counted between 2 & 2.5" each.
The problems that occur with overcrowding are more evident when the fish (or frogs) start dieing....but before that, a person will notice small things, like fin rot, sickness of all sorts, just an overall upset in the tank...This can be because of aggression of the fish, or poor health due to high chemical concentrations.
If you cycled the tank prior to adding fish your ammonia and
nitrite should both be at 0, but the nitrates climb quickly with an over stocked tank. Nitrates over 10 and this stress starts. Over 20 and it is actually unhealthy just because of the
nitrate levels. An over stocked tank can easily be as high as 80-200 nitrates !

This is why you need to test, and do water changes, as many as necessary to bring the levels down to a healthy reading.
Many of us have been through the very same thing, we speak from experience, and I can tell you for sure it is a lot more relaxing to have a healthy tank.
Most here at fishlore recommend the
API Master test kit for freshwater (liquid)....this is accurate, and has all the tests you need for most community tanks. There is a post I've seen just today about a special being offered....the price is well worth it.
Test "strips" are not reliable. Good Luck, I hope you can get this all worked out.