My dog has not been able to eat for about a month now and he don’t eat his kibbles and…

My dog has not been able to eat for about a month now and he don’t eat his kibbles and when I do wanna give him food he don’t wanna eat it only tiny bites , my dad said he noticed that he also don’t eat when I’m not home so maybe it could be because I’m not home ? But also he has had contact with fleas and they gave him 2 shots for the fleas to die on impact and also one for his stomach bc they said his stomach was hard so he may have a stomach problem. Please help me he’s so sad when I see my dog