I think you should seek as much help as possible. Do you have family or friends you can talk to?
Exercise and diet are more likely to give you an immediate benefit than the drugs. It will also feel that you are doing something about the problem yourself. You can also get 5HTP from health food shops, it is a precursor of serotonin, but do some research if taking that in combination with St John Worts and be careful about doses.
See your doctor to talk about the options available, any drugs they offer you will take some time to have an effect, 2 to 6 weeks, depending on the person. You will not be able to take 5HTP and SJW if you are on medication. Some drugs will be more effective than others and it is a game of chance of how soon you find the right one for you. The GP will first offer you the one that is most effective for the most patients and is also the cheapest to supply, this is usually Sertraline but varies. There will usually be some side effects, but these should reduce with time, but not always true, depends how sensitive you are. So it is likely to be at least 2 months before you can change to a different drug, and then another few weeks to see if that one works and is tolerable for you. They are generally relatively safe, and do help lots of people, but it really is your choice. No more unhealthy for you in the short term than a crap diet.
As above, CBT or counselling with the NHS will probably be some time wait, and it depends if you feel the person you are seeing is someone that can help you. If you can afford to go private then it’s worth a try, you can try a session or two and see if you think it will work for you with that service provider, if not try a different one.
Only you can figure out if there are people at your work who you could tell and who would be sympathetic to your problem. How about looking for a different job?
Good luck.