R.Z.
Hi T. :)
I have just gotten through a lot of the same stuff with my baby, now 11mos old. Of course, I only have one more, but still, I can sympathize with the challenges of attending to a demanding baby when their are other children around who have needs too!
Some of what helps is time. Soon, your little one will be crawling around, and exploring her universe, and will find less need for you. If you're like me, that will come as a MAJOR relief.
Also, know that you're doing everything right - a baby who wants her mommy is well-attached and may become more independent than your other children down the road. It's hard, but it's really the way we're designed as human beings.
Have you tried using a baby-wrap or a snugli, or something of that nature (sometimes called Babywearing)? I found that carrying my little one around in a backpack style snugli was sometimes the only way to accomplish anything. She *LOVES* it. And there are physiological and psychological benefits to carrying your child this way as well, especially when your baby is wanting you so much. Don't worry, she'll have plenty of chances to bond with her daddy too :)
Other things can help - like setting aside special mama & baby time every day, continuing to breastfeed (if you have been doing this all along) or bottlefeeding close to your body as though you were breastfeeding, co-sleeping - even just during naps. The more your baby knows she can rely on you, the happier she will be.
After about 9 months of not being able to leave the room without my baby girl screaming, she is now more confident and calm than my older daughter. I was even able to leave her in our church's nursery this past Sunday, which is something I was never able to do with her sister, until she was almost 2.
Hope that helps!