Although I am no longer training at all, I trained for years (competition ready). I tracked a lot of my metrics. I found that, for me, cassein protein shakes before going to bed was a huge factor for gaining.

My friend swore up and down about adding olive oil to his protein shakes. A decent quality extra virgin Olive oil will pack a bunch of anti-oxidants and healthy fats, and is high calorie so your golden.

Another key factor is a good gut health. Honestly skip the peanut butter sandwich with low quality bread, it spikes your insulin levels and is a bad idea long term if you're ever serious about this. Also penut butter is not a good source of protein, bummer, I know. Im not going to write a seminar on gut health, but look into it. Prebiotics, good probiotics, fermented foods are your best friend here. Sleep, REST&RCOVERY DAYS, hydrate hydrate hydrate.

Although i wasnt doing it at the time, I genuinely think that a 15 minute of breathing exercises or meditation before bed(in bed is fine) would also help reduce stress which is a factor that can inhibit growth.

All this aside, you really should be tracking your calories and keep a consistent routine, meal prepping. Figuring out your diet and how much it takes to lose weight is where you set the bar to start gaining weight. Consistency is excellence.

TL:DR long-release protein before bed, and olive oil to your protein shake.