My 5-m.o. Baby keeps on gnawing. Is it a sign that a tooth is about to sprout?

Yes, if she's gnawing on her mother's breast or bottle, she is probably teething. But take note that your child is in the stage of exploration so also putting objects to her mouth and chew on them. I've learned a lot of facts about teething from this site: http://www.parents.com/baby/health/baby-teeth/baby-teeth-frequently-asked-questions/ One important tip taken: always put on bib on your baby or have a clean towel within your reach - she will surely drool most of the time due to this milestone.