Wear fewer layers.
If you're sweating through your layers and soaking the inside of your coat in only five miles, you're wearing far too much clothing.
I also concur with this. But I would also add that well designed cycling-specific jackets are getting really good these days. With bibs to warm the waist and lower back and just a LS base layer, my Garneau jacket is really very good. Blocks the wind in front and wicks under arms and on back.
Garneau on sale now at CS!