@mamajaiy You have a PR for a close grip bench press... Just thinking about that hurts my shoulders. As others have said, you need more reps: 8-12 or 12-15 on some exercises.
Lower reps (with heavier weight) in the 3-5 range can be beneficial at the beginning of a workout on the bigger, compound lifts like flat bench, deadlift, squat, etc. although I'm personally a big fan of higher reps (5-8) on these most of the time. A single set of deadlifts at 315 lbs x 15 every now and then will leave your lats cramping and your hamstrings feeling like rubber. That's something you can try for yourself.
You should generally keep your reps higher on isolation exercises - focus on chasing "the pump" and "feeling the burn" most of the time, at least if your concern is truly body your body and not increasing the number of lbs on the bar. If you don't go above 5 reps for any exercise ever, I don't think you've even experienced what "the pump" really feels like. 3-5 reps of a dumbbell curl? That's something I might do once every 6 months, if ever. Personally, I don't like to go below 10 reps on exercises like bicep curls or tricep pushdowns, and sometimes I go as high as 20 (and rarely, 30!). I get a much better mind-muscle connection, and I can feel the bicep actually doing the work. I could be wrong, but I would put money down that your form on a lot of exercises, especially isolations, is poor.
For only 3-5 reps on a bicep curl, you're likely not going through a full and controlled range of motion
for every single rep and/or you use momentum and may recruit other muscles like the shoulders to move the weight. You're likely focusing on "moving the weight from point A to point B" instead of focusing on "wearing down the muscle". It's simply harder to control heavier weights on single-joint exercises for most people. Again, I can't know for sure without seeing a video of you lift, but I used to do the same thing myself, and most other people I have seen in gyms all across the country do the exact same thing. When it comes to building muscle naturally, increasing strength is important, but form, time under tension, and control have to come before adding weight to the bar just to say you lifted a heavier bar.
Generally, keep your reps slow and controlled, 1 sec or lift the wait, 0.5-1 sec squeeze at peak contraction, then 2 sec to lower the wait - a decent place to start. Do that over 12 reps, and you're looking at 40-48 seconds of time under tension for that set. You're probably not getting 10 seconds per set looking at your rep range and doing some educated guessing.
Also, as others have said, hitting body parts (or better yet, muscle groups) more frequently and with more weekly volume has been shown to promote muscle growth in natural lifters. I wouldn't tunnel too hard on cramming a split into 7 days specifically, but take something like the 3-day PPL, and try 3 days on, one or two days off, or 2 days on and 1 day off. I personally like Arnold's split: chest/back, shoulders/arms, legs and take a rest day whenever I feel the need.
Didn't mean for this to be as long as it did. Hope some of what I said helps. Nutrition is also a huge part of this, but that would take twice as long to expand on, and I feel like you were asking more about lifting improvements.
Tl;dr - lower reps (3-5) is fine for heavy, compound lifts at the start of a workout. 8-15 recommended for isolation exercises. Higher frequency and more volume are as important as increasing strength when it comes to gaining muscle for natural lifters. Also, nutrition.
Edit: didn't see the part about running higher reps earlier, so apologies for that. I still wouldn't change any of my recommendations on lower reps for compound lifts and higher reps on isolation.
Also, for chest development specifically, it needs to be hit from multiple angles, and tension over a full range of motion is necessary. Incline dumbbell bench press, weighted dips (not just at the end of a workout, bodyweight, to failure every time), incline cable fly (and other angles), with a nice squeeze at the top of every rep. Personally, I think the flat barbell bench press is a near-useless exercise in terms of building the chest. It over-emphasizes the triceps and shoulders, and very, very few people can safely lower the bar all the way to touching their chest. Dumbbells are king when it comes to actually building the chest: Incline, flat, or decline.