Seeing Improvements in Numbers, Not Body, Is That Normal?

I started working out regularly in December of last year. I had always had a gym membership and worked out occasionally, but it was lazy and sometimes I'd go weeks or even 1-2 months between workouts. But I decided to put together a plan, and I've lifted 2x/week for every week since then other than a 2-week vacation. I got a workout from my friend who's a personal trainer, it's a leg day, upper body day, and full body day, 6 exercises in each hitting all the big muscle groups, and I rotate through them in the same order, so every 3 weeks I do each workout twice. I do 3 sets and when moving up in weight will do 3x8, work up to 3x12, and then up the weight and repeat. And it's working, I'm getting a lot stronger, I'm very steadily increasing the amount of weight I'm lifting. But when I look at my body, it just looks the same. I looked back at a shirtless picture I took about a year ago and it could have been taken today.

Idk it's not that big a deal, I'm mainly doing this for my health, I'm about to have a kid (well my wife is), and I just wanted to be in better shape as my job is sitting behind a computer 40 hours/week. But I can't help but compare myself to others at the gym. Like I'm not even talking about the super jacked guys that look like they're on steroids, but there are plenty of relatively normal looking guys and things like their biceps or legs are just super well defined and you can see a visibly large muscle, and unless I flex that's not the case for me. Is this something that will come? Could it be diet related?