Could you post a photo please (and you might want to post it on the Growing Tomatoes forum here).

Yellowing of lower leaves can be caused by several things but the most common is over-watering.

However I'm concerned when you say it has only been transplanted for 7 days but is blooming and producing fruit. Could you clarify that as it would be very stressful for a 7 day old transplant to be blooming much less have fruit on it.

If it already had blooms and fruit on it when you transplanted it then most would have removed them before transplanting it to reduce the transplanting stress.

Dave

Sometimes the bottom leaves will yellow due to age. How old are the plants?

Numerous potential reasons.
Need pictures please.