Well first of all I have no experience in this area since I have never had sexual relations. But I have done a lot of reading on this forum so based on that I think I can give some advice. But beware, I have warned you of my inexperience
Anyway, from what I understand, the feeling that you have to "wee" is actualy normal. A lot of times when someone stimulates your G-Spot this is a feeling that you will get, but more then likely you won't "wee". Your best bet is to empty your bladder before you begin having fun.
Now more importantly, you just need to relax, stop worrying, and stop being so self-concious. If your worried about odor and taste, then just take a shower before you have him do anything. It seems pretty obvious that he wants to go through with this, and honestly, if he had a problem with odor and taste then I don't think he would be so eager.
Finally, I think the overwhelming shaking is because you are about to orgasim BUT I don't know for sure since...well...I'm a guy. You might want to research this or see a doctor. Yet if it this doesn't hurt you, then why not see what happens if you keep going
Above all just relax and enjoy yourself! Hope this helps!