If you added more than 20 percent compost, it might be a compost issue. Tomatoes are heavy feeders and need a lot of nitrogen and the compost may still be cooking. If the lower leaves are yellowing more than the young leaves, it needs more nitrogen.
Compost adds organic matter that feeds the soil web carbon, but they also use nitrogen. Compost that is aerobically made will also be alkaline which makes nitrogen less available and with competition from microbes and the nitrogen lost through volatization and denitrifying bacteria you could end up with a nitrogen deficit.
Young growing plants have the greatest need for the essential nutrients and the plants will translocate nutrients from the older to the younger leaves when it cannot get enough. So the deficit usually appears on the lower leaves first. You need to make sure along with the compost you add enough fertilizer to cover the deficit.
Being organic is all about balance. It is more complex than you think. If you add an akaline compost you need to add something acidic to keep the soil from getting too alkaline, If you add more carbon, you need to add more nitrogen to balance things out. If you add 20% or less compost can usually be accommodated. More than that, I usually have to add more acid or fertilizer to counteract it and sometimes adjust the watering.