Well......

All I can say is what cws already has: Your bag will turn up by Monday or it won't but contacting BA, BA holidays or anyone will make no difference to that. At this stage, your bag is part of a gigantic recovery system which has little to do with individualised human intervention, and where speed of recovery will largely depend on factors such as where it is now (was it stuck at your point of departure? Any given point of transit? Or has it actually gone to the wrong place?), why it was lost (was it just part of overall luggage delays or, for instance, has it lost its tag in the process), etc.

Incidentally, note that the very presence of medicine in your luggage might - in and of itself - slow down the recovery as it may attract customs or security concerns as a result especially if the medication is restricted and your prescription is not with the medication in the luggage.

In the first instance, if it were me, I would urgently contact my doctor, tell them about the situation and ask them what they recommend about the possibility of availing myself of the medicine locally. They will know or can find out if it is available where you are, what sort of prescription may be needed, and under what name it exists. They can also advise on whether there is something you can do to minimise risk if the medication does not reach you soon enough or if indeed it is a case of curtailing your trip to be safe, in which case travel insurance might or might not be of help. Priority no1 is your health, and only a doctor will help with that, not an airline or a frequent flyer forum.

And since the point of FT is that people start threads, but those exist and serve purpose beyond them and for many future readers who will do a search in the future, for everyone else reading this thread in the future except mtt:

Never ever put passport/id, cash or credit cards, phones/ipads/laptops, confidential documents, keys, jewelry, affectively or financially precious stuff,or indeed essential medicine in checked luggage!!!!!!!!!!*

*and if you want my advice, always keep a toothbrush/toothpaste, clean underwear, socks, and shirt/tshirt, phone/laptop chargers, and a pen or two in your hand luggage too...

**or if you want to "do what I do" rather than "do what I say", I actually do not check luggage at all whenever possible and travel with hand luggage only 95% of the time. it saves a hell of a lot of aggravation...