Hi Trish ....the 3 year guarantee is for shelf life....They are guaranteed for 3 years as new unopened markers. Once you have used them it depends on how much you color with how long they will last before needing a refill. Ciaos are the first ones that need refilling as they are the smallest (and least expensive) they hold between 1-2cc's of ink.
You should also make sure you are hearing a good "click" when you place your lid on...this is making sure your seal is airtight as the markers are alcohol based and would evaporate otherwise...
Sounds like you may need a refill....especially if you use pink a lot