Yea the save file is bloating. I'm not sure if it's affected by the settlements I built, because lately I do them more.
Here's a little known fact: for one reason or another the PS4 seems to have a baseline minimum size of 10.49mb for games. I've never seen a single game save that was smaller than that, and games who's save should be SIGNIFICANTLY smaller (looking at you FFX HD Remaster, with it's saves 10X the size of Vita version saves) wind up coming out at exactly 10.49mb.
From this we can assume that for most of the early hours in Fallout 4 your save would likely be SIGNIFICANTLY smaller than 10.49mb, and yet is being bumped up to 10.49mb because of this system peculiarity. That's why it looks like your saves are all size-locked and never seem to get bigger or smaller.
Bethesda game saves do get bigger though. The more you do, the more places you visit, the more the game needs to take care of. In this case the save file's reached a point where it's become larger than 10.49mb. From this point you'll actually start to notice your save regularly getting bigger in size due to the fact you can now see a more realistic "non-padded" approximation of the file size. Saves can shrink too, especially when you have a lot of zones suddenly reset (and thus get removed from your save) faster than you visit new spots.
At this stage there's nothing that says to me "unusual save bloat". You simply never noticed it before because save files can't seem to ever be smaller than 10.49mb meaning Fallout had plenty of time to let the save grow without you actually being able to notice.
If you're worried you have a genuine case of save bloat, keep a good close eye on your save file and then periodically check it to see how much bigger (or indeed smaller) it's gotten. If it grows very very quickly (say, to 20mb within a few weeks) you could very well have a problem, but if it's only a slow and gradual increase it's likely because you've got a lot of areas visited in your save which haven't had time to completely reset - try resting in a bed or waiting in a chair for 30 days to clear these out, resave and see if your file size decreased at all.