As little as it takes to make an impact. 50mgs should do it. there is research showing that short cycles hyper sensitize the pituitary to GNRH from the hypothalamus, which obviously decreases on cycle.
i know people, including myself (what a ****ing horror story) that this has worked for. i was shutdown in the manner you describe for almost a year. a short cycle and a regular post cycle therapy had me up and running sexually within a week. complete turnaround.
you can take the advice of others, but what i have stated is an option. youre just going to have to decide what you want to do.
i wouldnt recommend going to a doctor. they have no experience with this type of thing. They also tend to look at "ranges". if you testosterone level is 1 point above the minimum value hell just say "its fine". even if he doesnt, he wont know how to treat it. hell just suggest you "stop taking all supplements and drugs" and do a whole lot of nothing. i know, i have been there.