Why does my 99' Ford Explorer go through so much radiator fluid?

Hi and thanks for your time, I have a 1999 Ford Explorer Sport with a V6 SOHC. I got it about 2 months ago and it was running great! So I topped off all the fluids and noticed it used a full gallon of 50/50 antifreeze and still needed more, so I filled it up with water. The next day I went to check on it by pouring more water and it used up a whole gallon of water. Now I find myself filling it up with water at least 2 times a day. The weird thing is, when I got to take off the radiator cap, no steam comes out even with a hot engine! Do I have a problem with my head gaskets? It seems to run fine! Please help! I want this fixed now! Thank you!

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