I suffered almost the exact same symtoms as you. I seem to be ok
during BMT, then when i got posted to a combat unit I started to
feel like you do... extremely moody, homesick, miserable, don't
feel like socializing with my platoon mates etc etc.
For no reasons also I started to reminisce about times gone by my
primary school days etc... even missing my grandma who departed
eight years ago and whose death I thought I have long accepted... I
generally wallow in self-pity... to the extent that I was very
reckless during training in the hope that I will be injured and
downgraded.
In retrospect and reflecting inward, I am not used to the
regimental (and hectic) routines of a combat soldier and that is
causing me a lot of stress.
I often ask myself why I dont feel this way during BMT, and I
manage to know the answer after a while.
So how do I get out from this vicious cycle? I am also not sure.
But despite myself, in time I started socializing with my platoon
mates (those in combat will know that its next to impossible NOT to
socialize with your platoon mates... given the amount of time you
spent togather lol). That fostered some kind of comradeship and
give meaning to the things I do in my unit. The things you and your
platoon work towards, the pride when you have made some
accomplishments (like being the key platoon in securing the best
infantry unit for my unit, watched by minister somemore), and the
punishment you all have to go through when you screw up
(defaulter's parade anyone?)
These kind of activities slowly but surely washes out the negative
emotions and miseries in the early days of my posting... and by the
time we finish all 3 overseas training, I am a proud member of my
unit and my vocation...
Hope that you will overcome your depression in time... Just my 2
cents, but I think socializing with your platoon mates would be a
very good start!