I think dennis is right.
The greenhouse which I had is now sited in my neighbours garden because I got fed-up with the sort of problem you are encountering and he is now having problems with his tomatoes. Unfortunately, I have to keep an eye on his plants when he and his wife go off for a few days (sometimes weeks)
Small garden greenhouses are not ideal for growing tomatoes/ cucumbers/ melons/ etc because they all need a good circulation of air/ constant watering and a fully temperature controlled environment.
Ron