Call you parents-in-law the next day after you arrive at your parents' home. Tell them how long you are going to stay in China and ask them when is a good time for you to visit. This will give you some time to relax and rest before another trip. Why do you think 火车不干净? How long have you lived overseas? You can always buy more expensive ticket. Your family in China should know more about buses.
Don't worry too much. You'd be surprised how much our body remembers.