If you are interested in Maths and if you want to make a career in maths then Ms in mathematics, Ms in applied mathematics, Master in financial mathematics, Ma in mathematics , Msc in Applicable Mathematics  will be the post graduation degree for you .  You can be Data analyst  , Chartered Accountant , Accountant, Statistician, Data scientist, Teacher , Cryptographer, Operations Research analyst  etc :  You can start your job with bachelor's degree but it will be more great if you do a master's degree and then apply for these postions . 
If you have a interest in physics and maths  then you can be a physicist also . Also you can be a philosopher too .