Actually, I'll amend this. Bromocriptine DOES interfere! But I don't know if it had washed out of your system yet as in I don't know when you stopped taking it to know if it would still be involved.
I had the same thing with prolactemia years ago. I didn't have the tumor but they searched for one through MRI. I had an excess production of estrogen for my cause. Anyway, I feel for ya. It's a process to get diagnosed with that!
And now the positive pregnancy test. It's my understanding that pituitary problems can cause inaccurate pregnancy tests but it is very rare for it to do so. And medication can interfere but I do not see anything on bromocriptine specifically as something to interfere.
I'd say there is a good chance you really are pregnant. Call your doctor. They can tell you for sure. Let me know what happens!