Consider using the `ispell-parser' to check your text. For instance
consider adding:
-\(add-hook 'tex-mode-hook (function (lambda () (setq ispell-parser 'tex))))
+\(add-hook \\='tex-mode-hook (function (lambda () (setq ispell-parser \\='tex))))
in your init file.
\\[flyspell-region] checks all words inside a region.