You can rescue your supply (if this is what you want? ) You sound really upset. I think it's so unfair when a woman who has worked so hard at Bfing doesn't get to stop it on her own terms.
You have given your LO the best start and done so amazingly well. you should be damn proud.
Now, you may decide that it is time, and just focus on just getting the LO to take some formula and give yourself a break, but if you do choose to give BFing another go, there are things you can do, and I'm sorry (but not surprised) that your GP didn't suggest them to you.
first things first- you haven't been taking any cold and flu remedies, have you? My friend had ONE lemsip and nearly lost her entire supply. Decongestants are designed to dry up mucous (which is, kind of, what milk is!) AVOID. I'm sure you will also be aware that the combined pill is a no-go too.
Secondly, if you want to have a bash at getting your supply back, you can do lots of skin to skin and maybe try power pumping (be careful though- I ended up with a sodding oversupply after just 3 days of doing this.) www.lansinoh.com/en/help-advice/power-pumping-what-is-it-is-it-for-me
It was gushing out of just like it had been when my milk came in. My DS thought Christmas had come early 
Some people have had really good results using fenugreek (defo most effective when combined with increased BFing/pumping).
Jack Newman swears by Motilium (domperidone). It isn't available without prescription in this country, and sadly GPs are not licensed in the UK to prescribe it for milk supply reasons alone. It is a shame, as it works.
I am sure you know all this, but you should also drink loads of water and make sure you are rested and stress-free as poss (I KNOW- ridiculous suggestion when you're so upset and worried about this, SORRY.)
Good luck, and remember- you have done so amazingly to get to this point. You can try to keep going or not, but nothing will ever detract from that fact. Well done.
PS if LO won't take bottle, have you tried cup feeding? My DS was able to do it by 4m, although he eventually started taking a bottle of ebm not long after that.