After seeing to your symptoms, i think you might be suffering from muscular pain
(as you have suggested pain will vary on sleeping to lateral side). You can take simple analgesics with muscle relaxants. You have not mentioned about your profession, usually muscle pain
is common with heavy workers and also who sit for long time in improper position. As you said you are thin, just get checked your hemoglobin
in order to rule out anaemia
which is prevalent in the world. Your other problem ie thrush is nothing to do with this.