My pug puppy (6 months) has BAD diarrhea, & random coughing .. but is also in heat ?

Your puppy may have parvovirus. Take her to the vet as soon as you can get there. It may be too late to save her, but only the vet can tell. Really bad, explosive diarrhea is ALWAYS a sign to get to a vet immediately if not sooner. So is coughing. Coughing could also be pneumonia - but only the vet can tell. Take her in right away.