Hi Cara - I moved your question from the introductions section to the tomatoes section, where more people would see it. Welcome to the forum! Hope you find it friendly and helpful.
When the tomato plant flowers but then the flowers fall off without setting fruit, it's called blossom drop. If you type that in to the search box in upper left of most pages you will find a bunch written on it.
Basically it's a stress reaction, the plant is getting stressed, so it sheds the flowers to focus on plant survival. It can be any of a number of kinds of stress, night time temps too cold, day time temps too hot, too much nitrogen, too little nitrogen, too much water, too little water. You will have to think about what your conditions have been like to figure out what might be stressing your plant. When you say large pot, how large? Tomatoes do best with something 5 gallon bucket sized or more. Containers dry out very fast, so if you are having hot dry weather, you might need to be watering even twice a day. Of course pouring that much water through, washes out nutrients, so then they need extra fertilization....
If you really don't think the plant is stressed at all, the other thing would be pollination. If the flower never gets pollinated it will drop off. Usually nature takes care of that through wind and insects. But if you aren't sure, you can try hand pollinating. You can do a search for that too "pollinating tomatoes" and find what's already been written here about it.