Terrified about cancer head/neck - child!

To start with Cancer runs in our family big time! Not only my family (grandpa - grandparents) but also in my son's biological father's family! I may be paranoid or just an overprotective mother but I wonder something.  Okay first my son has had a really rank (baaadddd) odor coming from his mouth, he is 10 years of age.  We went to the dentist and got everything taken care of that we could, including taking a tooth out.  Well the problem persists and he is brushing his teeth.  He also has dark circles around his eyes under his eyes to be exact and they make him look like he is extremely sick!  He is pretty pale too.  I have asked a doctor in the past (with in the last 5 months) about him looking this way (although it was not as extreme as now) and they were like I am sure he is fine! I am soooo scared! They ran blood test about 7 months ago and it only showed low thyroid.

So anyway now on to more about why I think the bad breath is caused by something else.  I read on the internet that there are other severe medical conditions that could cause this and some not so severe (some life threatening).  Like one being head/neck cancer (brain cancer).  By the way my son has a motorized tic disorder (another story - I think it was caused by a medication he took - honestly I do - I have good reason to believe that).  I am terrified for my son and just wish they would run every single test they can to determine if he has any disease or illness!!!! I am about to cry right now!  Good thing he is at school.  By the way he has no clue that I am terrified and I don't let it show to him!  Please help!!!! No other doctors will help! Is there something I can say to them or is there doctors that will run all tests neccessary?  What could all this be??? I understand that anything told to me on here is not a diagnosis and I still need to seek medical services.  

Thank you so much ahead of time!

[xmelax35]

p.s. (sorry this is so lengthy) the odor coming from his breath literally smells like poop (fecies)  it has that nasty odor!