At this point in astronomy research, we do not know with certainty how many universes there might be besides our own, or if there are any other at all except for ours.
The multiverse line of thinking has not been proven, so it is a hypothesis. A hypothesis is just a guess based on some reliable information. The way we prove a hypothesis (an educated guess) is by finding evidence that supports the hypothesis. However, whether or not a piece of evidence supports a hypothesis is very intimately tied to whether the hypothesis was formulated logically in the first place, whether the connection between the evidence and hypothesis is logical, and under what conditions the evidence can be said to support the hypothesis. Basically, the connection between hypothesis and evidence has to exist, and has to make sense. Right now, there is simply no evidence (of which we know) that shows that multiverses exist.