hi Bad breath could be a sign of some systemic conditions too(gastric problem,sinusitis etc.)You can first get professional scaling and polishing done.Apply hi ora gum ointment (by Himalaya)on the gums.Try warm salt water rinsing three times daily for about a week .You will notice improvement.If not, then look for systemic causes.

Bleeding gums and yellowish teeth is symptom of gum disease. You need to get scaling/cleaning done as soon as possible.