Are these symptoms normal following a stomach flu? Could being on my period at the same time worsen my symptoms?

Yes, it is possible for symptoms like heaviness and weakness to continue even after a gastroenteritis infection. It is important to stay hydrated and get plenty of rest to help your body recover. If your symptoms worsen or if you develop a fever higher than 38°C in the next few days, it would be a good idea to see a doctor for further evaluation.