Cats licking their owners?

My cat Merryn is 4 years old but I have only had her 7 months. She has never been ill treated or neglected and I am still in touch with her previous owners and the rescue home who took her in briefly. She is classed as a Serengeti breed but is mostly Bengal in personality and siamese in shape.
We bonded very quickly and she has always been a very loving cat.
My problem is that suddenly in the last month she has started to wake me every night to lick my hands face and arms extensively. I have read a lot of explanations which I had already thought of i.e. the saltiness of the skin and a sign of affection.
I have three questions. I have to take a large amount of prescription medicines. Although I have seen no signs of any problem, could she be affected by them seeping through my skin like the salt? This is obviously the most important thing I need to know.
Secondly, has anyone any suggestions how I can change this behaviour without being unkind. I think it’s lovely for her to show such affection but I am suffering from sleep loss and I already have M.E. I have tried putting perfume on the parts she licks hoping the vile taste would deter her but it has not worked at all. Shutting her out of the bedroom is not an option as it would be a huge change and very unkind.
Last of all, can anyone shed any light as to why she has started this out of the blue after this long?
This is my first query on this site and it advises that you should put in as much effort into your question to get the best answers. I hope I have not made it unacceptably detailed.
Any advice or help anyone can give me would be very much appreciated.
Thank you.
Rainbowspirit :o)