Ok, lets banish a myth - The heavier you are, the more unhealthy you are.
I know people who are 10 stone but cant run for more than two mins without feeling ill. Wellbeing is very much about how you feel and it sounds like (scales aside) you feel good.
Having said that, on a B.M.I scale, given your height, 17st 11lb is putting you in the Obese category. Continue as you are and health issues will be more likely to occur at some stage in your life. Now, since giving birth your body, like many, has changed and losing weight may be more difficult (with a baby you will have less time to work at it too i imagine).
A holiday often kick starts us into a fitness regime, but dont worry if the motivation isnt there, enjoy the holiday regardless.
If you do decide to do something about the weight, start slow, dont rush and dont set targets at the begining as not reaching those goals can de motivate you further.
Adjust your diet to little and often and never eat until you feel really full, just satisfied. Cut out processed and saturated fats where possible. Eat portions of fruit and veg daily. Drink between 2-3 litres of water a day to flush you out and hydrate you. Take supplements like multi vitamins and green tea extract to boost the immune system and cleanse. Eat foods high in protein but low in carbs but do not cut carbs out all together, you still need them for energy.
Start by walking to places that are within walking distance rather than driving.
Once you feel the diet change is working, implement some regular exercise, but again do not become obsessed with the scales at this point.
Try 3 x 45 mins sessions of cardio a week, jogging, gym classes... whatever you enjoy.
After a month or so increase to 3 x 60 mins and continue increasing at a rate that suits you. After say 4 months, then begin to keep a chart of your weight, your body should be responding to the chages by now and the scales are likely to be more positive.
Good luck, remember small steps and you will get there