As above, get a gravity reading and if its close to what you were expecting (you know what SG you're shooting for, right?) then take another reading a few days later.
I'm interested in this 3+ month fermentation...That doesn't seem right, even if it was "slow," unless it had just started up again for some reason.
People will want to know, as do I, what was your recipe, yeast, etc? When did you transfer to secondary? Did you take a reading before transferring? It could be finished and you're just seeing residual gasses from the fermentation coming out of solution, though that may depend on what you mean by, "a ton of fizz." Pictures are worth a thousand words.
Or maybe there is something more fun going on...