I have a chocolate labe mix. She was a stray when we first found her. She was completely housetrained when we first brought her home and then she had puppies almost 2 months after we found her. Ever since she had the puppies she`s been peeing in the house constantly. She also has been drinking extreme amounts of water. She goes through at least a gallon to two gallons of water a day so we`ve tried cutting her water intake back but she still pees in the floor even if she was just taken out. Is there a good explanation to why this may be?

Has she been checked out by a vet since she had the puppies, or even since you found her?

Excessive water consumption can be a symptom of many different problems, the most common being diabetes or liver problems.

We are going to take her to the vet early next week. She was checked out numerous times before she had the puppies because we actually didn't even find out she was pregnant until just over 2 weeks before she had the puppies (the spca kept telling us she wasn't pregnant but was about to go into heat but they were wrong). She also has heartworms which we found out when we first took her to the vet, could that be playing a part in it?

A lot of dogs can hide a pregnancy very well, especially if they are only having a couple of puppies.

Yes the heartworms can be a factor.
What treatment is she being given for them?
Or is the vet doing something to up her immune system/health before starting treatment?

Due to financial reasons our vet recommended that we do the heartguard treatment. Its evedentally a new study that has proven to kill the heartworms by just giving the dog heartguard once a month. The only downfall is it takes approx. a year to actually get rid of the heartworms.
Plus the vet said she was in the very early stages of the heartworms which is one reason she recommened we do this treatment.
The vet also estimated that she would only have 2 to 4 puppies but she ended up having 8 which was surprising because of her size.

It depends on how severe the heartworms are.
I have heard of it working on a mild infestation but in extreme cases it actually does more harm than good.
The treatment is very, very costly.

8 pups! Wow, she really did hide them well, have the pups been tested for heartworm?

No, that was one thing we feared when we found out she was pregnant and had heartworms but the vet assured us that the heartworms could not be transferred to the puppies.