Bad breath or halitosis is often the result of gum disease and tooth decay. Dental issues can encourage bacteria to hide in cavities or pockets around the gums caused by conditions such as gingivitis and periodontal disease. 

If sensitivity is in the same tooth you had filling in then first get radiograph done for the same tooth to make sure it isn't approaching the pulp. If it isn't get the filling redone. All this depends on radio graphic examination. Bad breath can be bcoz of calculus n tartar or can be related to gastric issues or less water intake n long gaps in meals. So would need history to specify the cause

Sometimes it could be a deep filling which has not bonded well. You could revisit your dentist to get that checked. You can also try applying a small amount of Colgate sensitive prorelief or plus toothpaste over the sensitive spot for 1-2 mins and rinse it off. Use for few days and see if sensitivity reduces or visit your dentist again. There are various reasons for bad breath. Try tongue cleaning too and can use a mouthwash as an adjunct. If the problem persists, you need to visit your dentist again

Sensitivity may be due to wearing away of outer protective layer of enamel. For that you can start using toothpaste like colgate sensitive prorelief or sensodyne. And for bad breath get scaling polishing done. Also start using tongue cleaner to remove debris from tongue which also lesds to bad breath. Use interdental aids like floss or proxabrush to remove debris in between two teeth.