SAMe is good for some things, and not for others.

It has been my experience that younger patients do not do well with it, or get irritable with it.

SAMe is a substance that your body normally makes. With age, it tends to get low and supplementing it helps.
It will enhance synthesis of several neurotransmitters in the brain.

Using B12, B6, folate, can accomplish the same things if only minor loss of SAMe is an issue. These 3 vitamins convert homocysteine to SAMe in the body.

As Curious has found out, SAMe is great for arthritis and certain pain conditions. That is why I took it for so long.
(I am now trying a special Curcumin to see if I can get by with that for inflammation now). When I stopped the SAMe it appeared that I was okay for a while, but now my back is starting to flare, so it looks like I will be returning to it.(it has been about 3 months off it)

As far as your question, Blue, well, being in a bad mood is a rather vague description. Are you anxious? Obsessive?
Depressed? Does this happen with your periods?

Can you be more specific?