It could definately be Seasonal Affective Disorder, due to reduced sunlight... 5-HTP is certainly stronger than St. J-W, but they are different: 5-HTP helps synthesise serotonin, and SJW boosts it. But DO NOT take them together or take them with an anti-depressant (because they essentially do the same thing). Aside from that, you want to be careful eliminating carbs completely, because it will directly affect your serotonin levels. That said, you want to avoid surges in blood sugar which result in very low blood sugar level, which might increase the feelings of depression.
But, in general, whenever you alter hormone levels in the body with roids, you run the risk of anxiety or depression. Hopefully, this'll just be short lived as you body finds equilibrium again.