Re: Why have the number of clicks gone down but I have not changed my campaign?
There are many things that affect how many clicks you will get.
First, I would not look at the actual number of clicks. There are other more important metrics. The number of impressions may not be the same from day to day or week to week so look if the number of impressions has gone down. That may be your answer right there.
But more likely, your click rate has gone down or your ads are shown in lower positions which will definitely affect your absolute CTR and thus the number of clicks for the same number of impressions. This may be because other advertisers have better ads and/or increased their bids to get better positioning.
The most important metric is Quality Score. Everything in Adwords revolves around QS. It essentially tells you how well your ads are doing against competitors. It is used to rank your ads as well as determine how much you will pay. You want a QS of 7 and up. The main way to increase it is to have ads that attract the searcher and make them want to click on it.