PUP in heat?

[Nestle0905]

I think my 4 month old pup may be close to going into heat. She has been humping things. And the other day she looked swollen down there. No signs of blood, but she is fully potty trained and the last two nights she has had accidents. She never squatted during these accidents, she was circling around and barking on my comfurter and just began to go... I thought it was weird.
Any comments or help please let me know.