I fear the source of both of your problems is over-watering. Yellowing leaves is too much water and leaf-roll (where the leaves look like they aren't "unfurling") can also be caused by too much water. ballethel - tomatoes are seldom "maintenance free" ;) so you were quite lucky in the past. Now wth different soil you may have to be more careful as Dave said. At least until you have it tested and know more about its components, pH, and nutrient levels. Many things can cause plants to "shriveling up and instead of growing, the plants look like they are actually getting smaller" but excess water causes root rot and is the most common cause. Water only when your finger stuck deep into the soil is dry. When these dry out well and begin to recover, give them a mild (1/2 strength) dose of a balanced liquid fertilizer and then mulch them well. Contact your local county extension office to arrange for a soil test ASAP. Good luck with your plants. Dave

I can try to post a picture. It was getting dark by the time I'd thought about it. I'm sure to have more leaves like this tomorrow. I don't think it's too little water because the leaves never droop or wilt. They stand tall and strong.

I can't tell a thing from your photo. If in doubt, repot the plant in fresh mix. Increase the light. See if that helps. Jane

Thanks everyone for the responses! I was concerned because it seemed as if the leaves were yellowing/shrivelling up quite quickly. While the photo I posted on Monday didn't have any shrivelled up leaves, a couple leaves were starting to yellow and the plant has lost a large amount of leaves since I first got it. The temperatures have been between 15C-25C the last few weeks. Last week had some colder days so I had to bring them inside for few days. My plants are on a balcony so they get some morning light and late afternoon sun. At least 4 hours of afternoon soon - probably more. Thanks again for your help!