Hi there I was in your position a few years ago. Tumor in tongue, neck dissection etc... I'm a non smoker, non drinker and a veg head - it was a shock. You need to get into fighting mode. Three weeks is great - I was 5 and believe me I wanted to get it over with. If they'd told me you start tomorrow then I would have said that's great - thanks. My dr. is considered the top guy in Toronto - and he told me post op - in my opinion we got it all - but to be on the safe side I, sending you for chemo and radiation. I had clear margins too. The thing with this cancer is it can be aggressive and move quickly. There are a lot of factors to consider when determining whether you should go for radiation, your staging is part of it, also the depth of the tumor (peri neural involvement) the differentiation of the cancer, whether you had nodes involved and whether they were still encapsulated. Clear margins are fantastic, but cancer can exist and move on a microscopic level... Undetectable by a scan or the human eye, and because its not always predictable (often they can figure out where it will go but cancer doesn't always follow the same route - it's a very individual thing) radiation is a good idea. Radiation and chemo combined should kill anything left over, and it cuts the odds of recurrence in half.
Have they told you that you will lose your teeth? Or did you read that a lot of people here have lost them? I kept all my teeth. They will only pull any that are in bad shape and that they know you are going to have trouble with in the future (having to have a tooth pulled after radiation is a bad scenario. )
It's true that a lot of people have issues with their teeth post treatment, but good oral hygeine and diligence do pay off - so far so good. My dentist is quite happy at this point and I finished radiation almost 28 months ago.
I had three kids at the time of my diagnosis but they were older - teens and yum adults. I'm in my early 40s.

There are quite a few here like us, so I can honestly say you will get through this. And life will get back to mostly normal - it's been a couple of years and for the most part I've been blessed. I can eat what I want, speak very clearly (I'm told) in fact people who don't know I've had the surgery can't tell. I do have a few snazzy scars but they are a humbling reminder of what I've been through. I am active, work, and life is great.

Treatment sucks - I'm not going to sell you a falsehood, but in the long run it could be what stands between you and a recurrence so you will get through it and eventually get back to your new normal. It isn't instant, but with patience and kindness to yourself you will get ere. hugs.

Ps high protein (not all animal protein) helps heal. Try making yourself power shakes starting now, enjoy the food you like until your treatment takes at away that bit of fun - it's only temporary but you'll miss it.