The general rule of thumb for teething is as follows:

first few days: slightly grumpy and warm. "Hmm, I wonder if he's teething."

next few days: slightly grumpier and less warm. "guess he wasn't... maybe he's growing/constipated/stressed/tired."

next few days: very grumpy, more warm. Gums swollen. "Oh, it IS teething. Here's a cold gel-thing."

Next few days: still very grumpy, gums look red and shiny. "Man, this tooth has to be coming in like, um, tomorrow. I hope"

Next few days: Steadfastly miserable (all of you), naps are contracted, Calpol flows freely. White dot grows under gum. "Geez, the poor guy. It's okay, it'll be out tomorrow."

Today: darkened spot on gums shows where it will come through aaaaaaannnnnyyyy second. Murder-suicide contemplated. Nursing lasts >30 minutes per session. All ready to collapse. Calpol dosed by the minute.

Yeah, it's been fun.