Test, steroid, will make your LH even your FSH very low. It happened to me too. You'll need about 6 months to get back in normal range.
For the pituitary tumor, I'm not a doctor so I don't know, but myself I was very very low on LH also and my endocrinologist told me that with steroids it's completely "normal".
But if you are scare go for the MRI, since your LH was also low when you were not on gear.
Take care and good luck bro.