I read your query and I understand your concern.
A pituitary tumor could be related to many hormonal imbalance types, or not influence hormone levels at all, depends on the type of cells proliferating.
So Cushing syndrome could be a manifestation, but the amount of data you provided is not enough to reach into a conclusion. Irregular menstrual cycle could be one of the signs of Cushing, but could be present in other hormonal changes as well. In Cushing there are many other possible signs like weight gain, skin changes, hirsutism
, diabetes mellitus
, mood changes, muscle weakness
etc, the signs are so many really. Osteoporosis
can also be present to predispose to back pain.
The diagnosis usually is established apart from clinical signs also by testing for hormonal levels, if you've been diagnosed with a pituitary tumor usually those are standard tests.
I hope to have been of help.