Guitar Help

I'm having issues with my Yamaha acoustic electric. I've played guitar for a while, but my tech knowledge is pretty limited. If anybody has any insight, I'll take anything you got:

When I first got my guitar (about three years ago), I could capo it without the strings being pulled sharp (even using a Kyser), and the guitar had no buzz (with or without a capo). Now, I get decent buzz on the middle strings (particularly D over the entire neck and higher up on the A), and the capo pulls it tight, even adjustable ones.

I was thinking it might need a truss rod adjustment, but I don't know how to reconcile that with those two issues. The strings being pulled tight makes me think it might have too much relief, but the buzz makes me think backbow. Not sure what else could get thrown out of whack when it went almost three years playing fine.

Two things to know: I changed strings a couple months back from whatever came from Yamaha to custom lights (yes, I had the same strings for 2 years), and I keep it tuned to D standard.

If anybody has any thought before I take it to a guitar shop, I'm much appreciative.

Whenever a capo causes string buzz for me I just physically press the capo down until it doesn't buss anymore. If that doesn't work though I'm all out of ideas.

try putting the capo closer to the fret (closer to the neck than the middle)

Are you doing Chord formations in a way that you will not be blocking a string? Oh, 6 or 12 string? Something I have found out the hard way was, a 12 string needs a 12 string capo or else you cannot use the capo below the third fret without the lower E strings and the A strings completely buzzing when open. Otherwise, clean the fretboard off and make sure there is no obstruction after that, I have no idea.

Two things come to mind.
1. Check the bridge, see if it's intact and all good
2. I've experimented with D standard tuning, and it gives me some trouble in terms of staying in tune, see if the problem persists in E standard. If it does, you have disproven my theory

1st option : your guitar needs a set up, the neck curve and the action are not set up the right way. Please purchase this : Cruztools GrooveTech Guitar Player Tech Kit and refer to this in order to learn how to set up your guitar : http://www.fender.com/fr-FR/support/articles/fender-guitar-setup-guide/

2nd option : your frets are flat, they need to be reshaped or replaced by a guitar tech

3rd option : if you are drop tuning you can't really stay with a regular 10-46 gauge to keep in tune. The tension will be too small to have a good tuning. You need to increase the gauge a little 11-49 might do it for D standard. For exemple, I use 12-54 strings for a C# tuned guitar.

4th option : there is no fourth option.

Thanks for the comments, everyone. Very helpful.

Some of these things I've tried (pressing on capo, positioning closer to fret, checking the bridges), still same issues.

The most likely thing I'm thinking, based on the issues I'm having and the responses, is that it's probably something to do with string gauge/tuning and neck curve. Definitely going to see what happens in E standard.

Thanks again!