I have good oral hygiene but I have bad breath is this a sign that I could have something seriously wrong with me?

Most Likely Not. But possible if cause of odor is from your oral cavity brushing the tongue and proper flossing may help. You may also have sinus problems, diabetes, or digestive issues. All of these can cause odor issues. A dental exam first with a medical follow-up would be advised if not resolved.
Tongue scraping. Probably the biggest cause of halitosis or bad breath is the accumulation of bacteria on the back of the tongue. Look in the mirror and stick out your tongue you may see a white or yellowish coating on the back of your tongue. Tongue scrapers are available at any drug store that gently remove this layer of bacteria. Follow up with a good mouthwash and you will find a big improvement.
Probably not. There are many causes of bad breath, both of dental and medical origin. For more information see the website listed here: http://smilesapartcosmeticdentist.Com/fresh-breath-control.Htm see a dentist first who can refer you to a physician only if necessary. It should be easy to figure out the cause.