Welcome to the forum Sheils.
I am sorry to need to tell you this but you want no more fish at all for a while. What you have done is to get yourself into a fish-in cycling situation. Fish create waste that shows up as ammonia in the water. More fish means more ammonia. At around 0.25 ppm, ammonia starts to harm your fish. That tiny amount seems insignificant but it is no insignificant to the fish. What happens in a tank is that bacteria and other micro-organisms grow that can process and remove ammonia. It takes time for those things to grow. The process of developing the bacterial colonies is called cycling as a shorthand name in this hobby. On average it will take 3 weeks or more for your bacteria to develop to the point that you cannot easily measure ammonia in the tank water. During that time, the more fish you have the more water changes will be needed to control ammonia to less than 0.25 ppm. That is why I said no more fish right now. Now for the really bad news. Ammonia becomes nitrites which are also a poison, so even at the end of those 3 weeks you will still be doing water changes to control the nitrites. Again, the value that we use is 0.25 ppm of nitrite. It often takes twice as long for the nitrite processing bacteria to develop as it did for the ammonia processors. This time there is some good news though. The nitrites become nitrates when they are processed and fish tolerate relatively high concentrations of nitrates. Our typical advice is to do a water change so that nitrates never become more than 20 ppm above the tap water value that you read for nitrates. That is a far cry from the fraction of 1 ppm that we call out for ammonia and nitrites. That is easily dealt with by small, maybe 25% water changes once a week or even less with a light population like yours.
For detailed advice on doing a fish-in cycle,which is where you are, I have a link in my signature area for a thread that discusses it.