this might sound like a stupid question how many recruiting offices do you have

You currently have 3300 in stock, are using about 3900 for upkeep of units and produce a total of 5000 a day - including the newly built recruiting offices.

All seems fine... Judging from your build notifications, I take it you neglected the recruiting offices until the last minute

Hint (if you aren't aware of it): You can also build recruiting offices in conquered cities - gaining the very considerable fixed bonus they provide, representing civilians of other nations joining your military ranks.