my tomato plant looks heathly and is about 3ft high The problem is there are no flowers or tomatos on it

Hi Sandra and welcome to GoY. I've no idea why your tomato plants isn't flowering, and you wont get fruit without flowers! You aren't, accidentally, removing the flower buds?

Is it in enough light? Or, this may seem silly...are you sure that it is a tomato plant? I've known people to cultivate a weed that grew in the pot instead of the required plant! Try feeding it with tomato food to encourage flower production. Good luck!

Enough light is an essential but also fertilisation; it could be that the flowers have not been fertilised and then just fall off.