Hi R.,
I hope this finds you well.
Is it possible that he is cutting more teeth? I know after the first set of teeth, more than 2 can come in at a time and after the first two come in, the others may follow soon. It is also possible that because teething was a new experience that he is taking some time to get back to his schedule. I would stick with what you're doing and as with many things with our little ones, it will pass.
Six months is also the time when their sleep patterns can start changing, too. I think many babies sleep really well for the first 3-4 months and then start waking around 6 months. Give it another week, if you can, and see if anything changes. And maybe as you're doing, try changing things in his crib/room to see if that helps. White noise may help or a lovey? You may have already tried these things.
Finally, could he be hungry? I know at six months, especially on solids, most babies would not wake up to eat, but my daughter would wake up for a bottle sometimes if she had not had enough during the day.
As long as you can rule out any medical causes and have tried different sleep situations, it may just be a phase...
Good luck and take care!