Make sure you settle your resources, I see a gold, a corn, 6 fish, a pig, 2 crabs and a clam that are all unsettled in your territory, theres even an unimproved fish that
is settled. Yet another fish near Thapsus has been completely killed off by not razing that horribly placed city.
Resource tiles form the core of your economy, especially the food ones. Not making use of them will do nothing but prevent your empire from reaching its potential.
On this I will also state that overlap is not the enemy, its a wise thing to do in a large number of circumstances, and one of those circumstances is to claim food you don't yet have in a BFC!
I also notice that you don't have enough workers, just 10 for 13 cities is very low. The results of this are that your working quite a number of unimproved tiles, including a food, and you haven't been able to connect things up....
Also, although its not relevant to workers specifically but wow, I just noticed you don't have any fish connected
AT ALL