No, it’s not just you: Instagram went down for all users on both desktop and mobile at roughly 1:30 PM PDT. There’s no immediate sign as to what caused the downtime, but the company confirmed there was an issue at 2:08 p.m. PDT:
We're aware of an issue affecting Instagram, and should have a fix shortly. Thanks for your patience!—
Instagram (@instagram) May 27, 2014
Update: As of 2:42 p.m. PDT, Instagram was back up for most users. However, users have reported intermittent issues with posting and receiving new updates in the wake of the downtime.
An Instagram spokesperson confirmed at 3:11 p.m. PDT that the noted issue was fixed.