Unfortunately, the administration of a PPC campaign (especially one that is spread over more than one PPC search engine such as yours) can be a very time-consuming project.
As you have discovered, your competitors are constantly changing their bids on specific keywords and unless you are keeping equally constant track of your keyword placement, you could lose marketing dollars very quickly before you discover that you have slipped in the ratings. Your PPC search engine probably offers auto bidding, but it is still a good idea to not rely totally on just this one tool.
For a successful PPC campaign, you need to consider the use of one or more of the tools available that will automatically track your keyword bids for you and make adjustments without your having to sit at the control panel and watch the action yourself constantly. Many tools offer 15 or 30 day trial periods so you can see if they are right for you.
Check out our reviews of these types of products for more guidance on which are currently considered the best choices for automated bidding, which could save you an enormous amount of time as well as help ensure that you are not outbid within your pre-set budget.