Need help/advice about new puppy

[heather044]

I recently found this forum so I hope I am posting in the right place!

Yesterday, my boyfriend and I went to my old house to visit with my family. My sister got there saying there was two dogs that followed her up the dirt road.
For a little background information, this was in the country about 5 miles from town with very few people living on this dirt road and this was also the first time my family had seen or heard of these dogs as they know all the ones that roam the area, because they all have a home/family.
Maybe one of these dogs did have a home, but the other one came up to the house and would not leave. The other disappeared.
When we got a closer look, he has a pretty big sore on his head by his ear and he is so so skinny with no meat at all. We walked up and down the dirt road with people passing by us not stopping to claim him at all. With how many ticks were on him and how skinny he is, I don't think he has been taken care of for at least a month, maybe longer. We fed him a little and he was super hungry almost biting us to get the food down quickly. So, my boyfriend and I took him back home with us. He also had a collar on him, but it was about to fall off so it seemed like the collar was put on him before he lost that much weight. If nobody claims him, he will be ours. He seems to be around 3-4 months as he still has his puppy teeth. He also weighs about 28 pounds and we are thinking he is a Lab, but aren't sure if he is mixed yet or not and he is really tall!
We took him home, got all the ticks off of him, gave him a few baths to get him cleaned up, cleaned up his wound, and made him a bed. Before we took him home, he pooped once and it seemed normal.
When we got home though, we gave him some dry dog food as we already have a 10 month old dog, and we gave him some plain boiled rice with liquid worming medicine mixed in according to his weight.
Obviously, he was super hungry and ate really fast, but we knew not to let him eat too much at once.
Since we have no idea how long he has gone without eating good food, we probably fed him a little too much because ever since then, he has had really bad diarrhea. He hasn't went inside luckily and he seems to feel just fine. He is really friendly and energetic for the most part, just really hungry as we are trying to introduce it to him slowly.
We do not have the money to get to the vet to get him checked out just yet, so I am wondering if my other dog will be okay considering they have been playing and having a good time together. I don't want her to catch anything but we can't really separate them too much as it is just me here with them during the day taking them outside. I am not sure if it is from the sudden food he is eating or the worming medicine that is giving him diarrhea but any advice would really help us on what we could do to help get rid of or at least make his diarrhea better. Thank you!