Straining to pass a stool, after a few minutes instead of a stool a few drops of yellow-brownish mucous came out. Is normal with constipation?

YES. Mucous is the Bowel's way of "protecting" itself against irritants (that includes LAXATIVES... If you are using laxatives regularly (and I suspect you may be) STOP and see your Primary Care Provider for a GI evaluation! Hope this helps! Dr z.