I'm no expert at fitness or nutrition – trust me – I wouldn't have extra pounds to lose if I was, but I see a lot of you going from one extreme to the next with your diets and exercise, and I can't stress enough that you need to pace yourselves.
It's good to make changes, but the likelihood of a drastic change sticking is probably somewhere between slim and none.
When I started changing up my diet and working out about 3 months ago, I told myself that this time, I need to take my time with it, because every other time, I just stopped "eating bad" or started "eating healthy" immediately. This time, however, I implemented changes in phases – small phases. I started off at the gym, and did enough cardio to make myself feel like I got a good workout in. I then began to incorporate weight lifting after that as well as increasing my time doing cardio – but just a little – then getting in to a full on "routine". After I was comfortable with all of that, I implemented the changes to my diet, but I didn't go overboard. I didn't starve myself at 1200 calories a day, and I didn't switch from milk shakes to broccoli pops over night.
For some, habits can form by switching it up drastically, but I'm willing to be the number of people that can actually do that and stick with it are very low.
My advice…and I don't want to sound like I'm the "know it all"…is to make changes in phases – don't go all out all at once…trust me. You have a much better chance at succeeding by slowly developing this new habit of being healthy.