Hi welcome! Sure is a cutie! There is n way to know what breed of dog you own just by appearance alone. There are many breeds that can look similar to each other, so the only way to know if by having a pedigree on your dog.
As far as the skin issues, could be change in seasons, not sure where you are. My dogs coat changes colow throghout the year. 7 months old is kinda young for allergies, but it is of course possible. You can start on a grain free diet and find a protein other than chicken and see if that helps. Allergies can be anything protein related, grains, as well as the environment just like humans. I have even seen potatoes give some dogs an issue.
As far as size, dogs come in many sizes and since you have no idea what breed of dog it is, the best way to estimate is to double the weight of your dog a 4 months old to see what their adult weight will be. 1-year-old they are done growing their height and 2 years old for width, like how wide their chest is etc.
"There are two temptations to which people fall prey with dogs. The first is to think that biology counts for everything. The second is to think it counts for nothing"
- Tom Junod
“When you KNOW better you DO better.”
― Maya Angelou