Hello NameMatters,
You did not tell us if your domains traffic decreased, or if the average earnings per click decreased, or maybe both.
If you target the same sectors through your domains then there is big chances you had some months really lower than others.
A lot of businesses depend on the season.
For example: Real Estate, Rentals, Building, Remodeling, ...
Winter is the low period for most of these samples.
When the demand is low and the niche is very competitive then advertisers bid very high because they need to attract as much visitors is possible to continue having a minimum activity.
At the inverse when the demand is hot bids are seriously lower, some terms of lower interest are even no longer bidded.
Can you tell us the sectors you target through your names?
My basic recomendation:
"Do not put your eggs in the same basket!"
