Advice Needed: When a seller won't respond

Hi all! I'm having a bit of a problem here and wondered if you could offer me some advice. About a week ago, I won two items from a seller. (They have over 100 positive feedbacks) Both were a little over $100. Immediately after the auctions ended, the seller sent me two invoices. I wrote back and kindly asked if it would be possible to combine shipping. Three days later, I haven't heard anything back. So I try again, thinking that maybe the email didn't go through. This time I say that if it *isn't* possible to combine shipping to please still let me know. That way I know my emails are getting through. Two days later and no response again. So I check to see if the seller is active on eBay, thinking maybe they had a family emergency or something and aren't checking their email. They're still bidding/selling items! So I go to one of their items and send a message through "Ask Seller a Question." Today I check my email and nothing still. Payment is due within 2 days and I don't know what to do at this point. I don't want negative feedback, especially since I have contacted this seller many times AND definitely intend on paying. I could go ahead and pay for the items both separately but I'm wary of doing that since the seller isn't responding to my mails. I want to be sure I'll get my items. With that, I'm at a loss. Any advice you can give will be greatly appreciated. Thanks!

Take care,
~Shannon :-)~