I've taken both citalopram and fluoxetine am currently taking fluoxetine.
SSRIs take some time to take effect and for the first few weeks when you take them, you only get the side effects which can include nausea amongst other things that you can easily read about. The side effects vary from person to person and might be quite mild or even a bit irritating.
As far as the medication goes, I certainly don't see them as a cure for depression but I think they definitely useful for anyone with severe enough depression. I don't think they make me happy but they take the edge off the depression and get me more active and that helps doing the things that will get my mood into a better place.
I feel inclined to agree with your GP. There are many causes of depression and you even be right about the nutritional inbalance but with depression it really is important to deal with the symptoms before you can start dealing with the causes.
You may have heard about peoples' depression improving if they get more exercise, eat better or work with a therapist but if you are in a bad episode where you aren't even getting out of bed and can't face doing anything then there's no way you'll be able to do whatever you need to improve your mood.
As for the suicide risk, please remember that the people taking anti-depressants were already at risk from suicide. I personally am not sure if the drugs can be fully linked to the suicide risk.