You could seriously have an infection. If it's happened with 3 batches in a row, it's even more likely, unless you've changed equipment. An infection acts exactly like this - the bacteria convert more sugars and the yeast use them to make more gas, and it gets overcarbed. Ultimately you can get bottle bombs, and you'll probably get an off-taste. The beer will still be drinkable though, depending on your taste.
Make sure your OG is stable before you bottle. (I'm assuming you don't keg, or you could monitor the pressure.)
Being a little off with the priming sugar won't do this - you'd have to be pretty far off, like using the full amount of sugar for a half-batch.
If the beer is cold, and has conditioned for 3 weeks or more, and the glass is cold, I'd clean everything thoroughly and replace all the plastic (or use a different system) for your next batch.
Primary: Beer / Secondary: Beer / Lagering: Old beer.