Beware: I haven't had a period in nearly 3 and a half years. The last was before conception of DS1...now pg with DC3. Managed to get pregnant on 1st ovulation twice now. So YES YOU CAN GET PREGNANT WITHOUT HAVING A PERIOD! (and this time we were using contraception).
with DS2 I only knew because i started vomiting, was dead tired and burst into tears at anything.
This time was just v.emotional and developing a bit of a tummy. Didn't start sickness til after the tests.
Both times my periods didn't return until about 4 or 5 months after I stopped bf. BUT - that's me! My cousin got pregnant with her 4th baby while still exclusively bf her 3rd and no period - it was a bit of a surprise to say the least! If you don't want another one yet I'd strongly advise against relying on bf as a method of contraception!