Fan in greenhouse

We have not had much sunshine here for the last few weeks and everything in the greenhouse is suffering. All my toms seem to develop a white mould and the fruit rotted at the bottom, the cucumbers were not quite so bad had quite a few of them but it seems to have finished flowering now and has gone quite pale. I have a great crop of chilli's but quite a few of them are starting to just fall off and are rotting at the stem. I have had to put a fan heater in to try and keep the condensation down. Has anyone else had problems like these? I'm so disapointed after growing everything from seed.