I do not know how to do it pivot, as I only animate in GIMP, but try and find the place where it says optimize, and push it. Or save it as a gif, get GIMP: Filter>animation>optimize.
You are using Pivot, or? I do not know how to make the file smaller in that...
But if it is not larger than 1 MB, you can upload it to Photobucket. Right under where it says 'choose files' you need to select the 'Reduce to: 1 megabyte file size'
Optimized files is of course preferable, since they run better, but that will hopefully help you...
Uhm, when you are uploading pictures to Photobucket there's this big blue button with that text. You click that to select files on your computer for uploading. Below that, there's a multiple option button, that allows you to change the file sizes you can upload.
If you still can't find it, I'll provide a screenshot.