First of all, don't feel depressed about your body. I know it sounds cliche, but you have to learn to love your body. Do what you can to stay healthy and in shape so you have a good life. Be good to your body and your mind. Being depressed can cause issues with weight gain/loss, puts stress on your heart and other organs. Life is short and there's way more important things to obsess about than your breasts. I think at a point when we get over the age of 30, we learn we just have to accept our "imperfections". Things that I consider imperfections, my boyfriends have liked. No one is perfect and you can't sit around obsessing or being depressed over something that you can't change.
With that being said --- Everyone's breasts are different. One breast is usually slightly larger. I have D cup breasts but my nipples aren't really low - but one nipple is oval shaped and one is round. I have blond hairs that stick out of my nipples and over my breasts that made me self conscious being naked. I'm not a hairy person. I have no idea why i have these long blonde hairs on my breasts, but they are there. I tried getting rid of them but it made it worse. Most people don't even notice. I just don't pay any attention to it anymore. It is what it is. I am just a little fuzzy. lol
There are different reasons why your nipples could be low: It could be from weight gain and loss. If you were overweight while your breasts were growing they could gravitate more to the ground. If you were really thin and then gained weight and then lost weight, that will cause your breasts to "sag" or "hang", having lower nipples. If your weight continues to flunctuate it can cause it to go lower. Also, if you didn't wear a bra daily. And lastly, it could just be the way your body is made.
Exercise isn't going to make your nipples higher. Exercise will only make your pectoral muscles stronger and for woman with small breasts it can make it have a little more perk and look smaller, but it doesn't do much if you have larger breasts and nipples that are lower. It's still good to do the exercise to strengthen your chest but don't expect any perky results.
I'm going to be straight-forward and hope not to upset you - but you should lose weight. Your weight does not match your height for your Body Mass Index (BMI). Even if you are curvy, if you are 5 feet tall your target weight should be under 130. Actually according to the BMI calculator, it should be 128 or less. Weight will vary depending on how much muscle or curves you have when you lose weight and how your body is built.
When you lose weight, your breasts will also shrink in size. Unfortunately, your nipples will not get any higher with losing or gaining weight. But it will help with any back pain. Make sure you have a super duper strong sports bra that you can wear daily. I even sleep in mine. I have back pain with mine (mine flunctuate between a D and DD with summer to winter - I get pack on extra 10 pounds in the winter in Minnesota). A good sports bra makes a huge difference. --- Also if it has a thick lining, your nipples will not show through.
This bra - Danskin Sports Bra on Amazon is amazing! http://www.amazon.com/Champion-Womens-Powerback-Underwire-Sports/dp/B000OWC1I8/ref=sr_1_5?s=apparel&ie=UTF8&qid=1372097158&sr=1-5&keywords=danskin+sports+bra
It only shows the sizing up to DD online. You could do a search to find something similar or contact the company to see if they make a larger size you could special order. Also, if/when you lose weight, you may be able to fit into a DD. I'd suggest you go to a department store where they can actually measure your breasts and around your ribs. Most women are wearing the wrong bra size. This bra is the first sports bra I've been able to find that hides my nipples, gives me a rounded shape (instead of the uni-boob), lifts my breasts, has good support for even running, and has mesh for breathability.
The only thing you can do is lose weight, exercise for your health, get a very good supportive bra that has a nice shape like the one I just mentioned and learn to love your body -- and if you can't love it. Accept it. There are many other things about you that I'm sure are wonderful and perfect! And when you find someone that you love and loves you, they will love your body, whether your nipples are high, low, or one oval and round like mine. And if the person you date, doesn't like your body, then move on! Life's too short and precious to waste on someone like that.
If you cannot accept your breasts no matter what. There is the option of a breast reduction. I don't normally mention surgery but if you have back pain then it could help. With breast reduction/breast lift, you will have a scar around your whole nipple and then a long seam from the nipple down. Sometimes these scars do not fade. Sometimes the nipples aren't even. Some women would rather have low nipples instead of scars on their breasts. It's also kinda expensive. And again, you want to make sure you are in the right BMI range because if you have a breast reduction/lift and you lose weight later on, your nipples will move lower again with some sagging. And you'll still have to wear a bra regularly to keep from sagging as you age. Having kids - gravity will take its toll...
I hope I didn't offend you with my opinion and advice. Really.. I think you should just keep exercising, eat healthy, go to therapy if you are really depressed (individual and group therapy), and try to accept your body. Give it some time. Like I said, I think women struggle more with their self image, esteem and body in their 20s.
I wish you luck and good health.
And I don't know if this makes you feel any better... but always remember things could be worse. I'm 31 and just found out I have liver disease. I'd much rather have low nipples than have liver disease at 31 years old. Be grateful and happy to have good health and take good care of your body and mind. Wish you the best!