If you constantly have a bad taste in your mouth, it could be a sign of an underlying problem somewhere in your mouth. Bacteria are the major cause of bad breath and bad tastes in the mouth. The question is: Where is the bacteria hiding where you may not be able to get to it? It could be a new cavity or a suspicious area around a filling or crown.
Another possibility is that food is getting caught in an area which is not being brushed or flossed properly. Therefore, the first step should always be to brush at least twice a day and to floss daily. If the taste is still present after improving oral hygiene, call your dentist for an exam.
Finally, a bad taste could be a sign of gum disease (periodontal disease). Bacteria can reside in deep pockets between the teeth and gums. If you have not had a cleaning in over a year, schedule and exam with your dentist as soon as possible.