If you use the same pharmacy for your prescriptions go and have a word with the pharmacist and they will probably let you have 5 days supply to get you through.
You will probably have to sign for them and maybe even pay, but they do have the discretion to help in such cases.
Once you have got this sorted out it might be worth you setting up a repeat service, where the pharmacist in conjunction with your GP work together, and all you have to do is go and collect them on prearranged days before the last lot run out.