Instagram not only suggests posts that you may be interested in but also accounts you may want to add. If you don't want to see these, go to your profile and tap on the hamburger menu in the upper-right corner. Select "Settings -> Notifications -> Following and followers." Scroll down until you find the "Account Suggestions" section and turn it off to get rid of suggestions such as "[X account name], who you might know, is on Instagram" and other similar notifications.