Yes, you can definitely do it! It's totally possible, and not at all extreme, to lose 20 lbs. in three months.
After having lost 25 lbs. last summer, just as I had really gained momentum, I was suddenly sidelined from exercising in the ways I had become accustomed to by an, albeit relatively minor, injury. Feeling demoralized, I gradually gave up on my eating plan, and over the following six months I regained all that I had lost. A month ago, I resumed exercising, and since then I feel better and my clothes are looser. On Sunday, I resumed where I had left off with my dietary plan-- and I've lost three pounds in the last two days! Granted, it's probably mostly water weight; however, I feel GREAT from eating well and not too much.
There are a couple of quotes and signature lines I've noticed here that have really inspired me. I can't recall them verbatim, nor the names of those who posted them (apologies and thanks to them!), but they are:
1. Just because you fell down a few steps doesn't mean you have to throw yourself down the rest of the stairs.
2. Make commitment goals, not results goals.
3. It's about commitment, not motivation.
(Motivation is great, but it can be ephemeral. Commitment, on the other hand, can be renewed whenever you want. I think sometimes it can even be about committing oneself to getting motivated -- by posting as you have here -- or, for example, stimulating oneself with music that makes you want to move.)
Regarding belly fat, increased dietary calcium consumption, along with reasonable caloric restriction, has been observed to increase fat loss, particularly of abdominal fat. Dietary sources I really enjoy are low-fat Greek yogurt (e.g., Fage brand), low-fat BabyBel LaughingCow Cheese, and leafy greens. Natural Calm Plus is a good magnesium and calcium supplement, too.
By the way, you look absolutely beautiful and appear to have a lovely figure in your profile pictures. Don't worry about what your boyfriend will think and don't be too hard on yourself. I'm 28 and was at the weight you are when I was 20 (I read your profile info
. I weigh about a hundred pounds more than that now (eek!). In retrospect, especially from looking at photos of myself from the time, and from the perspective of now being 28 and over 300 lbs., not only do I think I really looked nice a lot of the time back then, but I also really wish I hadn't been so emotionally hard on myself and been so afraid of what everybody was going to think all of the time.
No matter what weight I've been -- from 135 to 365 -- I had never felt quite good (read: thin) enough, which made it feel perversely good to hide myself away and eat my way up to where I am now. This is not to say, of course, that you would be inclined to do anything of the sort, but from a very overweight 28 year old to an overweight 20 year old, I say love yourself and work hard at being healthy for yourself, and enjoy your life. Apologies for the didacticism, but I felt really compelled.
Good luck, and in the words of Dory the Fish, keep on swimming!