Coolant system losing coolant

I put 2 gallons of coolant in a matter of 4 months. Today I overheated, stuck in middle of road, walked and got coolant. Reservoir was empty. Started to put coolant in and as soon as I was pouring it it all came out from bottom onto road. I let cool down then I put some into radiator to get it to store. Then I filled radiator with water there was none and was full month ago, after that stayed at good temperature to got home, then tried to top off coolant and it didn't come out of bottom. What you think? Could it be bad radiator cap?