The first several years of puberty it is very normal to not have a regular schedule. I would suggest you get a small calendar and mark an X on the day you start. After 6-8 months you might start to see a pattern. For example, I remember a time when my periods went 26 days one month then 30 days the next, then 26 the next... and it just kept alternating. It felt like an odd pattern until I started tracking it. As I got older, the pattern changed, so don't expect it to stay the same. Stress, sleeping and how much you each can effect your cycle, so if it comes really early or much later than expected, don't let that freak you out. It's so normal.
I am 48 so have quite a bit of experience
. I have noticed with myself if I am dehydrated, the color is brownish in the beginning rather than starting just as red. It's very normal. All the cramping and maybe even headaches and irritability are all normal. My sister had such severe cramping she was bedridden the first day of her period, so even that is normal. She ended up taking birth control pills because it helps the cramping.
Let me know if that answers all your questions. I know it's a hard topic and it's good to know all you need to so you can relax about it.