Please try and see it as a blip and it is one day. If you are counting the dry days then mentally see it as X days minus 1 rather than seeing it as going back to the start of counting all over again.
Do you have an app on your phone where it records your non drinking/drinking days. They can be very motivational as it records days dry, units of alcohol not drank and money saved.
Do you attend any group settings such as CGL (Change Grow Live) formerly known as Addaction. This charity funded organisation is for all addictions and they run 12 week courses for addicts. They are really good and it helps to be amongst people that understand. See if there is one in you area.
The self help books are good and there are a lot of them out there. 'This Naked Mind' written by Annie Grace is good. I second the Jason Vale book as well. I have also heard good reviews on Russell Brands book.
5 months sobriety is a massive achievement as some people struggle to reach 5 days. Identify what the 'trigger' was to make you want that drink. Perhaps you were upset, angry, bored or seeing if you could really just have that one drink.
Remember that you take the first drink and the second drink takes you. If alcohol is your release for when things go bad (as it does) find something else less harmful that will take the place that alcohol used to fill.
Try not to dwell on the 'one day' and focus on all of the other days that you remained sober. Each day is a new day. I know just how hard this is. I am on day 25 and it requires dedication and strength and so much focus.
I will be thinking of you. Keep on going!!