First of all, congratulations!!! When I got my postitive with my son, I could only see the line if I flicked the test from side to side whilst holding it under the bedside table lamp, but I was definitely pregnant, lol! It will show off better in a couple of days.
I am now pg again with no 3 and very loosely following SW. I have a similar BMI to you - hovering around 25 when I got pg. I am not aiming to lose weight whilst pg, just to keep weight gain sensible (2 stone or less would be FAB!), so I allow myself to be generous with the healthy extras and have days off/extra syns here and there. I am not going to classes or anything, just following it at home.
There is a pregancy section here on the forum (where I keep a diary) - pop by for help and support.