Could also be fruit-fly attack. Where about are you ie climate, etc. Also, what's the soil like? did you fertilise before you planted, eg. fork over the soil? What was planted before you planted the tomatoes, you need to rotate your crops. You also need to keep the fruit off the ground.
B.

I'm in sydney.
Yes it was a very well fertilized herb garden before I started the tomatoes.
Definitely turned the soil before they were planted- they r only about 4 months old!
Do u think tomato dust might help?

Tomato get all sorts of viruses that will devastate them.
Tomato wilt virus is carried by hundreds of other common garden plants, petunia is one but there are hundreds.

Once they have the virus, they have had it.

Thrips will carry the virus from plant to plant.

There are some virus resistant varieties, cant remember the names.

Touching tobacco then your tomato plant will almost certainly infect the tomato with virus.

There are so many other problems that knock tomato as well, soil fungi, two spotted mite, heat.

One way out of he problem is to grow cherry tomato, they are a much tougher plant all round.

I see you have a woody mulch, that will drag the free nitrogen out of your soil, no problem as long as you top up with some more N.
Ca NO3 is good because the Ca will help control blossom end rot, yet another killer of tomato

In Sydney it really is too cold for tomatoes now, at least in most suburbs especially away from the coast. I grew tomatoes almost every year for many years near Frenchs Forest and learned from experience (and my teacher at the Ryde School of Hort.) that it was generally a waste of time planting before the last week in August. Once I got away with planting toms in mid August - a very mild winter, and once I tried the last week in July and they failed completely. Plant the last week in August to early September and you'll have the bulk of your fruit before Christmas and miss the Qld fruit fly. If you've fertilised, rotated your crops - rotate tomatoes following leaf vegies; beans, etc., not any of the solonaceae family (potatoes, capsicums, etc.). I think your fruit is struggling against the cold. Oh, and with mulches, leave them to rot down on the surface, never dig it in; even with fertilisers, blood and bone etc, work it into the soil at least a month to 6 weeks before planting.