This fizzyness is due to either:
bottling too early
using too much priming sugar
infection.
Bottling too early, always check the sg is stable over 3 days (and make sure you are fermenting in the correct range for your yeast.) Lagers need extra care if you are using a lager yeast at correct lager temperatures. They ferment slower under these conditions. Many experienced kit brewers leave ales for 10-14 days in primary before they contemplate bottling.
Using too much priming sugar. The correct amount is 6-8gms per litre. Or, a teaspoon per 750ml longneck and 1/2 a teaspoon for a stubby. If your beer bottles ar 660ml, or your stubbies the smaller 300ml, you may wish to back this quantity off a bit. Also, during fermentation, there is alot of carbon dioxide produced, most goes out the airlock, some stays in solution, this is why, when you float your hydrometer in the sample test tube, lots starts to form on the hydrometer and it floats higher, the longer it stays in the test sample. If you bottle very quickly after fermentation has ceased, this CO2 is added to the CO2 from priming. Once again, leave the brew in primary a bit longer, or back off the priming. Many people have reported problems with carbonation drops, the results are variable. I suspect one brand is better than another as some people report no problems with drops.
Infection. Your beer will slowly increase carbonation over time, leading to churning on pouring and eventually bombs. Sourness, loss of flavour, yukky flavour and gushing are all symptons.
If it is infection, either pour it out or keep all bottles in the fridge and drink now.
If it is just overprimed, you can release the pressure in PET's easily. Just partially unscrew so the gas escapes, then seal back up before the beer escapes. Do this a few times over a few days.
Glass botles can be easily released too. Use a bottle opener that has a bar across the top of the crown seal and operates on a few of the crimps at once. Very gently, ease up a few crimps a few milimeters, let the gas out, and let the lid resettle. Usually the lid will reseal, but about one in 15 will need to have the capper run over them. Do this a few times over 3-4 days.
One trick when pouring overprimed bottles is to wet the glass first with water.