We have found that after our beer has been bottled for several months that it has a very large head on it when we pour. It doesn't matter how slow we pour or how angled the glass is - it foams up like crazy. Are we doing something wrong or does this happen often with natural carbonation?
Have these bottles been in the fridge for at least a few days to force the CO2 into the beer? If not try that. Otherwise the beer is either well over carbonated or an infection has gotten hold. How does the beer taste/smell? If it tastes like beer and smells like beer then it's most likely over carbonated.
How much beer did you prime (Finished volume)? How much priming sugar was used, did you weigh it or measure it out, the former is much more accurate.
A little more info on your bottling process would help:)