Im pregnant and my doctor told me that i have central hypothyroidsm and i looked it up and u get that from having a tumor. is that the only way?

No: That arises from any condition that prevents the release of certain hormones from the brain that tell your thyroid gland to release its own hormone. A tumor is one possibility. There are many other possibilities, some hormonal for instance. It is important to repeat testing and to test other brain hormones as well and likely an MRI will be ordered to check for anything there