You don't have to have CO2 in order to grow many plants. I built a beautiful heavily planted Jungle aquarium in a 125 gallon tank with no CO2 added.
Look in to fertilizer (like seachem flourish) and try some more species of plants. Not all plants you have will do well, so find some that do.
Also, if your aquarium is new, it make take a while for nutrients from the fish to build up in the gravel to feed your plants. Ours was pretty slow growing at first.
Look at some more easy to grow species of plants like anubias, java fern etc.