fish oil aint a drug. there are lots of natural sources of omega3 fatty acids.
if you are looking for natural substances that promote mental health then there are many like folic acid, sam-e and vitamin D.
check your p doc before you start this stuff 'cause it might affect the way your meds are working now.
example: i am not allowed to take grapefruit juice anymore because it makes my cholesterol lowering drug too powerful and increases side effects.
in my supermarket there are eggs from genetically engineered chickens that lay eggs containing omega3s. i have no idea if they help mentally. i try to eat a varied diet that includes fish. if you eat too much fish these days you get a mercury problem which is most dangerous for preggers.
so its hard to know whats right for you without personal advice. g'luck
pi