I think it's been mentioned before, but we should all keep in mind that we're still pretty heavy in the conference season. BookExpo was this week, right after Memorial Day, and there's been other conferences all April/May etc. And, while agents do pitch sessions and such at these, they're also trying to find homes for their clients' books. If they find an editor interested in a client's book, that's naturally what they're going to focus on first (but don't worry, someday we will be clients!!!).
Lenore, go ahead and follow-up again. Don't see it as being awkward--it's being professional. Just say something along the lines of hi, I sent you my requested manuscript [title] on [date], and was wondering if you've had a chance to look at it. Thank you for your time, Lenore. If you're worried if she's receiving your emails, try from a different address, or send snail-mail. Agent Janet Reid suggested making an address that includes your name so you're clearly not a spammer (no animechick918 or such)---it ups your chances getting into an inbox, and Reid says she mouses over emails in spam to see the address--if it's a name, she'll look at it.
I've often heard three months for a partial, six for a full...if you haven't heard anything from the first follow-up, send another. Patience and stubbornness. Of course, if it happens many many times, you may want to look elsewhere.