are you working out in a commercial gym? with a personal trainer from there as well? are you currently fat, or thin.

to be honest, lack of strength gain from my own experience is always down to the standard 3,

1) lacking intensity. personal trainer in commercial gyms tends to change workouts however they like. which is a problem if you want to gain strength.

2) not eating enough (if you're thin) or not eating correctly (if you're fat). how crazy we're talking about this eating 2-3 hours. a whole meal or just a standard snack like a packet of biscuit.

3) not having enough rest.

so there's your answer i guess.

i'd suggest for you to suggest to the trainer to focus more on strength oriented workout. weight training, free weights, reduce the machines or even don't use it altogether. i hope he doesn't ask you to do all those kettlebell swings etc (basically crossfit shit).

standard strength oriented workout
1) lower down the rep range (from 8-12 to 6 - 8)

2) sets, depends either from 3 sets to 5 sets

3) workouts should center around big 4 lifts, OHP, Bench press, Deadlift, squats (basically the bosses of the compound movements). you can add dips (weighted if bodyweight is too easy) and pull ups (weighted as well if bw is to lmao easy). these workouts, i'd suggest you to go for the lower rep range as mentioned above. once done you can add isolation workouts as accessories if you with for hyperthrophy.

4)lets say if you can rep 3 sets of 5 with the same weight, increase it on the next workout.

again i'm saying this based on my own experience. unlike some dude who thinks he knows it all, i'm not gonna say that i know best. but happy to say that i actually gained some strength even during my cut following this hybrid strength and hyperthrophy workout.

make sure to work on your form as well. hopefully your trainer is good enough to help you on this. i've seen PTs in personal gyms letting their clients work with half rep benchpresses and squats, which is abit sad.

For the meal, i can't comment much to be honest. you said you're not fat for your height but can't see any abs, so you're in the skinny fat range. since you are more aware of what you're eating, you can try continue doing what you're doing now and see how's the progress on your strength training goes. of course the best way is to track your calories and macros. this need a little bit of effort to start at first, but gets pretty easy once you get used to it.

goodluck

Well it is a strength routine so your first and foremost goal should be getting stronger. I'd target being able to bench press and squat your body weight and deadlift at least 1.2 times your bodyweight for starters.

The standard benchmark that's used in 4chan fit message board and even Reddit (lol troll message board) is 1/2/3/4 plate (Google this). You can achieve this, I dare say you're already alot stronger than 90% of ppl in the gym.

Supplements, from my own experience, getting your protein intake up was a good start. And you're on multi vitamins too. Unless you're doing fasted training, don't bother with bcaa. Post workout, just eat a banana or white bread or any other fast acting carbs. Preworkout might be a good if you're having trouble getting into workout mood. But if you wanna save money, just drink coffee (no sugar).

Again, if you want to see solid result, tracking your calories and macros will be your best bet. You go to any bodybuilding, powerlifting forum, the first thing they'll ask you will be "what are your macros" then only they'll ask your routine.