Twins!!! Found out today!

Marilu. • 33 years old. Expecting #4. Its a boy!!!!!
I'm very excited but I had a feeling I could be carrying twins! Beautiful heart beats at 162 each! For those moms having twins or multiples have you found a site or a book that provides info? I tought I knew everything about pregnancy (it's my 4th) but have no clue on differences. Let's make a thread! I'm 8+2 and babies dated 7+3