You’ve half answered your own question.
You’d have to be very lean at 155/160lbs at 5’7 to be anywhere near your “mass limit”. So that’s not really what’s up.
What you are eating sounds good. Lots of variety, fruits + veg and good sources of protein. However when it comes to gaining/losing weight the total calories consumed is what will determine your success. Also worth tracking or keeping protein high to maximise favourable body composition changes.
If you’ve not been gaining much then you’ve certainly not been in a consistent caloric surplus.
Consistency is what makes diets work. You hear about the hardgainers who eat like pigs and can’t gain weight they do it half the time. Eat big one day then eat small the next and you’ve stayed exactly where you are. Same with those are a bit on the fluffy side. Diet one day then go off diet the next and nothing happens.
It’s long term adherence that is effective. Consistency and discipline with every single day done right a step in the right direction. Days, weeks, months or even years as long as it takes just keep taking steps forward. You go off track doesn’t matter you’ve only set yourself back a day.
Even if you don’t count macros if you eat similarly everyday it’s easier to change your caloric consumption by consistently adding and subtraction stuff.
I’m not a big eater myself but some things I’ve done include a big glass of milk after every meal. Even if you are almost full from the meal I can always quickly down some liquids.
Seems like you get plenty of protein. You can eat more of that if you want but carbs will fill out your calories effectively too e.g soft drink or fruit juice
Lots of things you could do: More eggs, more chicken breast, post workout shake, more carbs intra/pre workout, pasta (more calorie dense) replaces other carb sources, snacking on food or drink etc.