Have a non malignant tumour in my pituatary gland, but the past few days have had a really bad headache, haven't had that for ages. just worry.

Talk to your doctor: You should talk to your doctor soon. It may not be related to the pituitary tumor, but it might be time to do a repeat scan or blood work to see if things have changed.

Tumor Bleeding: Sounds like what used to be called pituitary apoplexy. Besides headache there can be endocrine complications like dangerously low cortisol production ( addisonian crisis). You might need a MRI and/or blood work asap.

I'm worried also: Hemorrhages into pituitary adenomas are quite common and can announce themselves as severe headache. You should perhaps get seen.