Hi,
Is the swelling just in your fingers or does it happen in other extremities as well (e.g. feet?). If swelling happens everywhere, it may be worth letting your doctor know. If just in your hands, do you keep your hands above your heart while exercising (like at a 90 degree angle) or let them drop straight down. Keeping your hands elevated above your heart and moving your fingers around should help with swelling. Also, make sure you're doing a good cool down and stretch afterward your treadmill time. Thirty minutes sounds like a long time to be swollen after exercise. While stretching, try to find ways to keep your hands elevated (stretch while lying on your back and pulling your legs towards you so your hands are high).
As for sciatic pain, losing weight can help, but also stretching your IT-band and doing other stretches for your hips, hamstrings, and quads might really help. Do you belong to a gym and use a treadmill there? Maybe ask a personal trainer to see if they can show you various stretches for these muscles?
Hope you stick with the program. Dealing with pain and swelling makes exercise hard, but I think it will pay off! Good luck and kudos for you for getting back in shape. Not only for yourself, but to also be a good role model for your son! Also, do talk with your doctor about your current situation, your goals, and what you've done so far to meet them and the obstacles you've faced. Every person is different so general advice may not necessarily apply to your personal situation. Again, good luck and good for you! Take care.