HI!
First off, just learned by being here...
Most people do not get MRIs until around one year, still having problems, or at their insistence or if they have a superdoctor. It is nice for peace of mind though or to also check for neck injuries. I did not get one till 11 months or so. I would not be too concerned that you did not have one, unless symptoms increase rapidly.

As far as antidepressants, I feel I have to label myself as a non- med taker unless necessary So I will go out on a limb and say
1. You are super early in recovery. Flat affect is normal in head injuries and will pass with time.
2. I think a lot of chemical stuff goes on in our brains after head injuries that heals.
3. From my personal experience, I tried antidepressants because of headaches, but they made me terribly depressed and side effects were awful. I waited a long time before I tried them.

As Mark said, the small dose for headaches is different then a dose for treating depression.

I think that docs like to give meds out and I just feel that it is too early for you. They want to do a "treatment" but you just need time.I think that Mark's natural suggestion is great.

For you I would pass on the pills! Your symptoms are normal and will get better. The pills will always be there if you choose to try later. For me I felt that my body always did best with the least medication, most rest and good vitamins.