suddenly not sleeping?

My boy did so well sleeping in his bed for the last few months but all of a sudden he's not staying asleep for longer than an hour and once he wakes up wakes every ten mins! I don't know what to do?! He's not having a wonder weeks, started solids a month ago and changing to formula two weeks ago with some breast still. He's 6 months old and only used to wake once! I'm so tired 😩😩😩😩😩