HI there plantmother, and welcome to Scarleteen!
I'm sorry that things have felt painful when you've tried to masturbate before. Usually when folks experience pain when they touch their vulvas or vaginas, it means that the very sensitive skin is irritated, usually because there's too much friction. Whenever someone sexually stimulates those areas, they want to make sure that there's plenty of lubrication, either natural (as in, the fluids that glands in the vagina produce when they feel relaxed and aroused) or synthetic (lubricant that they've gotten from a bottle or packet that we've applied to themselves). If you don't experience that wetness when you masturbate, it may be a sign that you need to take things a little slower and fantasize/stimulate other areas of your body some more.
As for what you're describing inside of your vagina, in all likelihood that's just normal vaginal tissue or even a little bit of leftover tissue called the corona. You might want to read through
Innies & Outies: The Vagina, Clitoris, Uterus, and More as it gives a lot more details about these parts and what they might look like. You also might find
Going Solo: The Basics of Masturbation helpful, as it also has tips and tricks.
I hope this helps!