You are only at 3.5 weeks post-birth. Give you body a chance to deal with the many things going on with you and the baby. As long as the baby is getting enough and you are pumping after feeding her, you are doing well. Try not to supplement formula and instead cluster feed (keep nursing her when she needs food) and your body will catch up to her demand/need.
There are many Mother's milk tea that you can find at your local natural food store to increase you milk supply. Drink lots of liquids and eat well. Another thing that helps is the herb Dill in either the fresh herb form or seed form. You can eat the seeds directly or make a tea from it and drink it. There are may recipes on the web for the tea. I did the herb directly and my friend ate the seeds. We were both successful at nursing for 10 mons to 14 mons.
I worked so I did the pump and store thing. Are you using a machine or manual pump? If it is a manual, get a double breast machine. If you have a machine, make sure it does both breasts at the same time. Oh, when you go back to work and pump at the office, take a picture of your baby. Just looking at your DD and thinking about her will help with the let down and help you get more from your pumping.
Just do the best you can and don't beat yourself up about it. There are many babies that only had formula and they are fine. Remember, your love is the best thing for you baby and the fact that you are working so hard to get info to try to nurse your baby tells me that she is already a lucky little girl.
Regarding the gas, watch your food intake. Keep a food diary and see if she is more gassy when you eat certain foods. Then you can avoid or cut back on them as feasible. I used Gripe water to help my son with his gas. Worked great.
So breathe, relax and enjoy your baby. Good luck.