Health Anxiety…can anyone help?

I have recently had a baby (4 months). I am finding myself thinking about death alot…i am very fearful that i have some kind of terminal cancer. I have been to the Dr a few times recently over various aches and pains although nothing very consistent apart from a niggly back pain. The Dr has put it down to anxiety and has only agreed to do the basic blood tests to try and relax me. But it won’t. I want a test/scan to look for something more in depth. I don’t know whether to try and get help for anxiety or to keep on at my Dr to try and get the tests done. Please no scare stories….i am on the verge on a panic attack. Thanks in advance