Is my 7-month-old female dog humping because she's in heat?

If your female dog isn't spayed, she could be coming into heat causing this behavior. Female dogs go into heat around every six months, and if you have had her for five months, it would be about time to go into heat again. This behavior will continue every six months unless you get her spayed, which I highly recommend getting done. Best of luck!

This behavior is often considered part of a dominance issue and can be seen amongst any dogs, even neutered dogs occasionally. Be aware that your puppy will be able to mate very shortly and you should consider neutering her or making arrangements to keep them separated for 3weeks when she comes in heat next

You are correct that Panda could start going into heat suddenly, as female dogs can start their first heat any time after six months. If you don't bland on mating Panda, I would get her spayed as soon as possible.

I recommend you have Molly seen by your vet to make sure she is okay. Dogs usually go into heat around 6 months of age, but can also go into heat earlier, and often the first heat is not noticeable, as there is not always a lot of visible discharge. She may be pregnant, so speak to your vet about what your options are regarding that as well, and if you want to keep the puppies to term. I recommend having Molly spayed and your other dog neutered to help reduce the risk of unwanted pregnancies, certain undesirable behaviours, and certain diseases. See the link below for more information: https://www.avma.org/public/PetCare/Pages/spay-neuter.aspx

I wouldn't be alarmed by this as it is likely a behavioral problem. Mounting, thrusting and / or masturbation in dogs is a normal behavior. However, excessive amounts of this can be problematic and may need to be addressed by a behaviorist. An occasional episode of humping should not be a cause for concern and neutering does not always fix this 100% of the time. If it becomes excessive, I would research a behaviorist in your area and schedule a consultation. Please feel free to contact me if you have any further questions / concerns

Great questions! Dogs can go into heat for the first time anytime after six months. It is never recommend to breed a dog on their first heat because they aren't fully mature emotionally or physically. It's best to breed them on their second or third heat for the first time. Speak to your vet about screening Mia for potential genetic health problems, and whatever dog you want to mate her with should have the same done. This prevents genetic diseases from being passed to the next generation. I hope this helps!

It is highly unlikely this is a true heat unless the first one was very short (3-5days; often referred to as a split heat). I would be concerned she may have an infection which the male is confused by. A full vet check and possibly a sample of the fluid being passed to be examined under a microscope would be recommended in order to determine exactly what is going on and to treat appropriately