argh when am i due?

I found out two days ago that im pregnant with my first child, i had a 3 week long period starting the 17th of march, brought on by stress and high blood pressure, the doctor said im 4-5 weeks pregnant but could be anything up to 9 weeks, ive registered for a midwife to contact me, but im so eager to know how far gone i am, will i have to have a scan to find out and whens the earliest do u think ill know?

oh and does anyone recommend a good book about pregnancy and newborns to help me get through this, i guess u could say and instruction manual!! haha! im so excited but im scared i hope being a mum comes naturally i want the best for this child!!