Be aware, that sometimes there is a difference between the number of clicks you see in the advertising service and in Google Analytics.
The list of possible reasons of this:
The landing page for your ads is not being tracked. If the landing page for your ads is not being tracked, your campaign information is not passed to Analytics. Ensure that you are tracking all landing pages for your ads.
Your landing page might redirect to a different page. Redirects in landing pages can often keep the Analytics code from launching and properly identifying the traffic as having come from a paid search campaign.
Users return to your site via bookmarks with UTM-tags. Google Analytics records traffic from these bookmarks like arriving from your ads. However, the ad platforms don't record the clicks (and advertisers are not charged for these sessions since they're not actual clicks on the ads).
Google Analytics tracks sessions, while ad platforms tracks clicks and impressions. If a user clicks on your ad twice within thirty minutes without closing his or her browser, this is registered by Analytics as one session, even if the user left your site and then returned shortly after. For example, if a user clicks on your ad once, clicks the back button, and then clicks your ad again, ad platform registers two clicks and one impression, while Analytics registers one session.