Yes, you need to see a dr to find out why they are irregular but it would make it harder to figure out your cycle.
I did, but miscarried. I have poly-cystic ovaries. My aunt has the same she has had 3 children. My cousin has it she has had 2.
Of course you can. As long as you are having periods and having unprotected sex there is a chance of getting pregnant. I suggest you see your doctor. They can give you birth control pills that will not only regulate your periods, and protect you from getting pregnant.
Yes, you can. It may be unpredictable, but you can. Also, irregular periods can be a symptom of polycystic ovaries, and you should get that checked because PO can cause infertility, and many other physical symptoms such as facial hair, weight gain, etc.