Hi,
It depends on the solar cycle. The Sun has an 11 year cycle which is defined by the number of sunspots. Right now were at the low point in the cycle and so often there are no sunspots on the Sun. When were at the high point of the cycle there can be more than 100.
During the high point of the solar cycle (called solar maximum) there are many more CMEs. The average is about 140 per month. During solar minimum (the low point of the cycle) the average is about 40 per month. However, they tend to be clustered in that you have a bunch and then a bit of quiet and then some more. The other thing is that the big and fast CMEs (more likely to cause space weather) occur much more often at solar maximum.
Best,
Christina