I've recently had numerous tests like bloods & mri's but all come back clear. i have a lump on back of neck and head always feels heavy, tired always.

They can't find any: Thing wrong! this is the title of a book and a bigger theme in medicine. Assuming you indeed have had all the tests, stress could be the cause of the head heaviness and fatigue. Stress can cause a lot of physical symptoms. Appropriately, you've had tests and seen doctors to exclude a serious medical condition. Now you need a doctor to help you with stress and tension, most likely.