Akuma pretty much tackled the major issues here, I'll just add for further clarity...
Your body belongs to only one person: YOU. Choosing to share it with your partner is a choice you consciously make, and that includes what you allow your partner to do with your body. Pretty much as Akuma said you need to make sure you are comfortable before going somewhere, if you aren't comfortable talking about it, you won't be comfortable doing it, this is pretty much true for everything.
Some women don't feel comfortable being stimulated down there at all by anything but a penis (sometimes not even that), I've known women that think it's disgusting or weird to be fingered or rubbed down there, or have someone perform oral sex on them. It's all a matter of comfort level.
The other thing to consider in this situation is are you uncomfortable with the act itself? Is it something you would personally do to achieve your own pleasure? From what it sounds like, you and your partner are fairly new to this "sexual territory" with each other..... you may just by uncomfortable with the idea of having sex with him.... which doesn't mean he's not right for you, maybe it's just too soon in your relationship for this. You need to question what you want out of this relationship, do you really WANT to have sex right now in this stage of your relationship? Your own needs and desires may be different from his, and that may as easily be the culprit for your uncomfortable feelings as just being uncomfortable with the act itself could be.
Hope this helps :)