HANG IN THERE, mama! yes, it's all of the above (toddler, can't communicate, hormones, etc.), and IT WILL GET BETTER! it might get worse for a while (i don't know when your new baby is due), but this time next year, i promise you will be looking back and wondering how you survived...
just take it day by day, minute by minute if you have to. can you find a local kid, either after school or a homeschooler during the day, to be a mama's helper? not a baby sitter... just someone else to read to her (and that's fantastic, btw! she's absorbing sooo much from that...). this helped me save my sanity with my toddler years! even a 10 year old kid will be fascinating to your dd, and give you a breather.
signs and talking will help, and she's learning more about those every day. it sounds like she's one of those kids who will be real quiet for months, then one day just start spouting whole sentences (my oldest was like that). i thought he was brain damaged or something, but it's just how these kids work. your next kid might be babbling at 9 months, like mine did... even though they come from the same place, they are sooo different!
you're doing a great job, mama. keep it up, just surrender to the tiny tempest that is your toddler. she's just as frustrated with you right now... this is both of you learning the wonderful dance of living together.
i must admit... when ds has driven me to the absolute limit, i will pop the They Might Be Giants ABCs DVD on (we don't have regular TV, just a monitor for movies). this will mesmerize him, even in the middle of teething. i hate myself when i do it, but it keeps me from losing my temper. sometimes i just need a few minutes where he's not grabbing my boobs, not throwing another book at me, not shrieking because i wouldn't let him stomp the cat's tail...
do whatever you have to to get through this year. it will be full of frustration, but there will be days you are just sooo in love with your little one, i promise!
good luck, mama!
katje