You can have up to 6 additional email accounts in Comcast besides your primary account. Sign on to your primary account and click on the Users & Settings tab at the top of the page. You should see a link in blue underneath your user name that says Create Secondary User.
Some tomato plant leaves yellow due to a lack of sunlight on mature plants. When the plants become large, bushy, and heavy with fruit, the top portions of the plant can block the lower portions from getting sunlight. This can cause the leaves to yellow, and is really nothing to worry about.
The most likely culprit, I think, is going to be item (3) above. At least, that is what the problem is in my large tomato garden 95% of the time when leaves begin yellowing and/or curling. If you have bacterical speck, you will notice tiny specks of brown to black to almost purple on the leave surfaces.