Howrse: how often can you breed?

Well, I can't buy and trade horses yet (I've played this game a year ago, but now I had to start all over. I'm 3 days in now and I can only trade and sell horses when i'm level two, which means I have to wait 7 days!) So I decided to start breeding my own horses. So far I have successfully raised two foals. Now, it's not letting my mares breed again. Is there a certain amount of time you have to wait after a mare gives birth before you can breed it again? I'm NOT inbreeding, that's not the problem. It's just, whenever i click the "public coverings" button for the mare, it just takes me back to the top of the page. It doesn't even have a message or anything, it just takes me back to the top of the page. What's going on?