Acoustic guitar fret buzz fix?

I have an older epiphone acoustic and ever since I messed around with the truss rod and changed string guauges, Ive had fret buzz around twelve to fifteen fret area. specifically on the thirteen fret of the B string. I went back up to eleven's hoping to fix it and its so close to being back. any ideas? I never messed with the bridge or nut so we should be able to get back there. I think it came with twelve gauge strings but those were too heavy for me so I went to tens, then settled on elevens recently