While we can't say for certain what you're feeling, although it does sound like it might be your vaginal corona (which is another name for the hymen). While the vaginal corona is a flexible membrane rather than a brittle one (it doesn't actually break in the way that many people assume it does), some people have one that's on the thicker side, or one that's not all the way worn away when they first encounter it. You can get a sense of what the Corona looks and feels like here: My Corona: The Anatomy Formerly Known as the Hymen & the Myths That Surround It
. Have you ever done a self-exam with a mirror to see if that helped you figure out what you were feeling? And have you had a visit with an OB-GYN?
Too, it may help to know that painful sex, whether that's vaginal intercourse or something like manual sex, has a lot more to do with things like communication, relaxation, and lubrication than anything else. You can read all about why that is here: From OW! to WOW! Demystifying Painful Intercourse