Why is my pizza coming out "soggy"?
First of all, like Max said you should definitely be cooking your pizzas at a higher temperature. In any case, this doesn't sound like an oven problem. If the more toppings you put then the more watery your pizzas get, it would only makes sense that your toppings are releasing water. Even if you strain canned mushrooms they will still retain a lot of water. Some cheeses have a lot of water in them, but this mostly happens with fresh mozzarellas. In general I'd say experiment by cooking pizzas with only one topping to see which are releasing water, then make the necessary adjustments.