I’m sure others with more experience than me will come along shortly, but my main concern here is your mental health. I’ve also suffered (currently on anti-d’s) so I know how hard it can be and my opinion is that your mental health needs to be your priority. If you have felt as down as that then I think a visit to your doctor is needed (please please go).
As for the diet side, 10 pounds is a great loss. I know you are disheartened but there are many many stories about people just like you (and me) who have slow/stopped losses that restart again in a few weeks allowing them to lose much more. I’m on week 5 as well, and I’m not far ahead (12 lb’s lost) in fact you say almost into week 5, at the end of week 4 I was only at 11, so only 1 lb different to you.
In the BSD book, He does suggest around 4 weeks in to consider if the 8 week diet is right for you as it doesn’t necessarily suit everyone. During this period where you are not feeling well maybe it isn’t right for you but only you can decide that. It might suit you better to go on the 5:2 for a while until you feel a little better? It would be more constructive and more healthy to allow yourself to eat more of the right foods, rather than giving up altogether.
I wish you all the best and if you need help with your depression I really hope you get it. I think it’s great you have mentioned it and recognise it, too many people won’t speak about it, and it doesn’t help. In my opinion mental health needs to be more openly discussed.