If she just had a heat a month ago and is in another now, I'd get her to the vet ASAP. Same thing happened to my aunts pitty (now fixed, never bred) and she actually had a pretty bad infection for her first "heat." She ended up having cysts in her girly parts (thank God they got her fixed when they did). Try to find a low cost spay-neuter in your area...possibly contact your local humane society as they often will do it pretty cheap. See if there are any rescue groups in your area that may be able to connect you with a low cost vet.