In my first floor bathroom there has been a smell of sewage, or as if someone just used the bathroom for a BM. The smell comes and goes but has been getting mor frequent. Is this something I can fix easily or is it muych larger problem?

You have a sewer gas problem likely due to a bad trap or vent, maybe even a bad wax seal on the toilet. What plumbing skills do you have and do you know where the trap is located?