I don't think your diet is a big problem. Protein intake is enough.
Besides, you have been exercising for four months, and exercise time is not a problem. I think you should find the reason in the exercise method. I think the problem may appear in the following two aspects:
1, your posture is not correct, so that the force point is not completely placed on the chest muscle;
2. The dumbbells, barbells or instruments used are not heavy enough, and the muscle fibers are not fully stimulated, so that protein cannot be fully absorbed from the body.
Because fitness is a practical project, everyone's system is different and their genes are different. If you have the conditions, I suggest you find a personal trainer to take you to practice several times. If conditions don't allow, I suggest you buy a fitness magazine like a bodybuilder and adjust it according to the movements in it until you find a posture and movements that can fully stimulate your chest muscles. In this way, the circumference of the chest muscles can be continuously increased through practice.
I hope my answer is helpful to you. My QQ number is in my profile. You can also add me. I am also a fitness enthusiast. We can have regular exchanges and discussions. Wish you success!