Five pictures being 100 Mbytes doesn't sound right at all. It's easy to work out what it should be in total. Just add up the sizes of all your JPEGs and add a small bit for the text (a few tens of K), and that's how larger your .web file will be.

If you're loading huge RAW, PNG or TIFF files say, then yes 100Mbyts is easy to obtain - not many pictures of 25Mbytes each say are required to make 100M or more.

If you are importing RAW images or some other extremely large uncompressed format, then you're advised to use the Optimize Photo function which compresses and down-converts them to more reasonable resolution and JPEG compresses them. Check out he Photo handling chapter in the manual, I think it's covered in there.