Ive been on antidepressants for about 30 years, several different ones beginning with the old style amytryptaline with its delightful side effects. They are not addictive, ive tapered off them easily for weeks or months at a time on several occasions, but i became depressed again each time as i have intrinsic depression which will need to be treated permanently, which is not usually the case, i think a year or two works well for a lot of people.
Anyway I've been on venlafaxine for several years now. In my experience the mood doesnt improve for several weeks with these modern antidepressants which have very few side effects however. To be honest, i think the older style amytryptaline made me feel somewhat better quite quickly because, besides the dry mouth and urinary retention, the other side effect was basically zonking out after taking them each night. I think i felt better just because there was some relief from the terrible insomnia i had and rest from the constant pacing around of thought in my mind.
Anyway it takes time. On the other hand, your dose seems miniscule to me. I have seen a psychiatrist who upped my dose from 150 mg to 225 mg as he correctly determined it was not reaching a therapeutic dose. The difference was quite marked. Whilst i am in no way recommending a dose as high as mine, i do wonder if you are having a therapeutic dose. Or maybe, if the dose is lower it could take longer to start working. I know two other people on vanlafaxine and they are both on 150 mg which works very well for them. A quick look at the British National Formulary will show you the dosages advised so may be worth checking how dosage is determined. This is something i would encourage you to discuss with your gp in an open manner. I have always done so with many different drs over the years and they are always happy to take your feedback on side effects and efficacy into account.
Finally, you can and will get better! This is an illness with symptoms affecting not only body but also the mind in all its aspects, all due to unusually low concentrations of certain neuro transmitters. Venlafaxine is good antidepressant as it boosts both seratonin and noradrenalin by slowing their breakdown. Give it a few weeks if you can. Discuss pros and cons of increased dose. You may then try another one as some work for some people not others, thats true, but its a little early to determine that yet i would suspect. Hope this helps.
"Darkness visible" by william styron helped me a lot if you have any concentration, which i know is extremely difficult, but its a short book and rich in content so even reading the odd paragraph may help. Just because when you read it you know he understands and it helps you see that you can and will recover.