My Journey... What to do about Self Sabotage?

Hi all,
I'm wondering if there are other people who have experienced some of the same issues I am going through and would be able to offer some emotional support and advice.

So, as a kid I suffered with weight problems. I was always the "chubby" girl - I had to have my mother hand sew me jeans that were big enough because the clothing for the other girls never fit me properly. I always felt compared to my sister, who was always slender and tall. At around age 13, I really started to lean out, and I believe this was partly due to hormonal changes, as well as a long period of depression which decreased my eating. At about age 16, I switched from bag lunches to school lunches, and gained about 30 pounds in one winter (I'm 5'4", so that is quite a lot on my frame). At about that time, I began to become interested in health and fitness, and began educating myself on nutrition and fitness. For the first few years, I tried running (which I was never really into), and also joined a gym. I was mostly a cardio queen, but I was building my confidence in the gym (I always HATED sports and gym class in grade school). All of this did very little to help me lose the weight I had gained, and I remember finding it very exasperating, and I kept searching for new answers.

At age 18, I did the full program of P90X, and ate according to the meal plan. I didn't lose a single pound on the program (others have lost 20+ lbs on it). I did gain some lean muscle. I chalked it up to a learning experience. I went off to college, still feeling unwell in my body and wishing I could lose those pesky 20-25 lbs I had gained in high school. I began to learn more and more about weight training, and fell in love with it. Power lifting was my absolute favorite, and it came very easy to me. Sophomore year, I changed my major to Health and Fitness, and was working out 5 days a week, eating a clean low carb diet. I felt myself getting fitter and losing a bit of fat, but I was still holding onto a 27% bodyfat percentage. I even got a job as a Personal Trainer, and was successful in helping others lose weight. I was strong, but none of this was helping me slim down so that I truly felt happy in my own skin.

At age 21, a chronic illness caused me to quit my job, drop out of school, and basically I laid in bed for a year and a half wondering what was wrong with me and if I'd ever feel better. Amazingly, I managed not to gain much weight during that period. Funnily enough, it was my knack for nutrition research that helped me find a cure for my illness. I am now turning 23, and FINALLY getting back into a gym routine.

I have NEVER been fully comfortable in my own body. I cannot understand why I have such a hard time losing body fat. I often wonder if I am self sabotaging, as I have all the knowledge about fat loss and exercise that anyone would need to get in GREAT shape. Maybe I have a fear of failure, or some sort of complex left over from when I was a chubby kid getting bullied for it. I feel like all of my "failures" to drop the extra twenty pounds were just learning experiences to get me prepared for the time when it will actually work. I need to be able to do this for myself. I've been trying to lose this same 20-25 pounds since I was 16, and now I'm 23! It seems ridiculous to be unhappy in your own body for so long, when I have all the knowledge to do it. As excited as I am about it, there is always something that stops me. I get sick (which happens often), and after a week of illness I no longer have motivation or belief in myself. I cannot pinpoint what is stopping me from really committing, but I really need help with it. I know losing those few extra pounds isn't a cure-all, but I know it would make me feel like I could do anything in my life that I wanted to. What do you all think? Have you ever been here, and what did you do to overcome it?

Here are my stats/workout/eating regimen in case you were interested:

Height: 5'4"
Weight: 166
BF%: 27.5%

Workout:
Upperbody Strength 8-12 reps Monday, Thursday
Lowerbody strength 8-12 reps Tuesday, Friday
Moderate cardio directly after all weight training sessions
Looking to incorporate sprinting onto off days

Nutrition:
No processed sugar, no dairy, no gluten
Mostly lean proteins, Low GI Carbs (sweet pot, a bit of brown rice, quinoa), lots of veggies, a bit of Low GI fruits
Healthy fats (coconut oil, etc)
At least half my bodyweight (oz) Water/day

Thank you all for reading my ridiculously long post!