I did it, At 39years old decided to try for another before I was 40, Already had 3yo dd and 4 year old ds. Took me longer than expected to get pg, and then had miscarriage (my first). But got pg two weeks later and now my 6month old ds2 is playing happily beside me.
On positive side, he is the most gorgeous happy easy going boy and everyone is besotted with him. So much so that it has made me want to ttc no4!!!!! Both brother and sister love him and it is wonderful to see them with him.
On the negative side, it is more difficult dealing with three than two children, activities like going swimming with them is not so easy trying to watch three is much less safe than watching two. Getting out in the mornings is much harder, but I am hoping this will get easier later on.
Fortunately I had not got rid of all my pg or baby things, so finacially it is not so bad. Am using resuable nappies etc again too. But I am sure that the finacial issues will be worse when they are teenagers.
It is harder to get family tickets for things with 3 rather than 2 children.
But I went ahead and don't regret it. So I hope that you have success at either getting rid of the broodiness or getting pg!