I'm 38 and stuck between 11.5 to 13.5 st for the past 10 years. Occasionally I manage to lose a bit and move back towards the 11 (I want to be 10.5 ideally), but then life interferes and I get back over 13.
With a coccyx problem, swimming might well be a great way to move without putting pressure on it. And not just doing lengths (I used to plan my current garden needs and design my dream house as ways to overcome boredom doing lengths - I don't do underwater music!!). But do some other exercises when in the water - sideways stretches, running on the spot (a lot less pressure with the water buoyancy) etc. If they have an aquafit type class, go once to get an idea of what would be good and then do it yourself on your own trips. And don't worry about your swimsuit - everyone (even those who have great bodies) have some hangups about it and most people are too busy concentrating on getting their own stuff done to look at other people anyway. There's all shapes and sizes in the pool at my gym 
Add lots of veg into your food if you can - if you're having pasta with a tomato sauce and chicken, add in some mushrooms, peppers, courgette and peas for example. Or cauliflower chunks and carrots and mushrooms to a curry sauce, along with your meat. Do you eat salad at all? Add a bowl of leaves to the side of meals, or a few tomatoes, or nibble on olives rather than crisps.
My lunches at least 3 times a week for work are a salad bowl - but I hate dressing and am hungry, so it's: 2 carrots in large rings, half a pepper in pieces, handful each of sugarsnap peas, olives, cherry tomatoes, handful of lettuce shredded (I like romaine for a bit of flavour) and half an avocado if i have some (i only buy when on special). Avodado has some fat, but it's very good for you. If' I need more than that, I have packets of breadsticks in my desk to nibbble on.
And if you are hoping to lose weight, perhaps don't buy too many clothes for now - concentrate on accessories instead if you are buying anything. A nice scarf over plain white t-shirt and stright jeans makes a plain outfit look chic, some nice earrings or a belt can also change the look of something. Find things about you that you are happy and comfortable with, and highlight those with jewellery (doesn't have to be expensive) or other accessories, and that will often minimise bits that you don't like.
And on clothes, try to dress for the size you currently are (and suiting your body shape). Not the one you hope to be (and if possible, not the larger one you were). Dressing the right size and shape can actually take POUNDS off how you look (I had a suit once in a size that fitted me well rather than pulled tight or hanging baggy, but was also long line so drew the eye up and down rather than sideways - a few girls asked where I'd bought it as they loved it (chainstore) but were ASTONISHED when I said what size it was, thinking it was 2 and sometimes 3 sizes smaller!!)