He prayed in a direction opposite to the qiblah out of ignorance
Question

I am a young man working in Makkah, and my family is in Jeddah. I used to stay in Makkah from Saturday till Wednesday, and on Thursday and Friday I would go to my family in Jeddah. One week I went to Jeddah, and found that my father had changed the design of the room where I sleep; he had blocked the door through which I used to enter the room and had opened a door in the opposite wall, and he had changed the furniture in the room. Praise be to Allah, I used to offer most of my prayers in the mosque, but sometimes I missed the prayers (in the mosque), so I offered them in my room. One month after these changes have been made in the room, I found out that I had been praying in a direction opposite to the qiblah. What is the ruling on that? A reminder: I only go there on Thursday and Friday, and I offer most of my prayers in the mosque.
Praise be to Allah.Facing the direction of the qiblah is one of the conditions of the prayer being valid; a slight deviation from that direction is overlooked, but a large deviation is not. Also, one who tries his best to work it out and gets it wrong is forgiven. What appears to be the case from your question is that you did not try to work it out and you did not ask; rather you did not pay attention to the changes made in your room that caused this confusion, so you have to repeat those prayers.
If you cannot work out how many they were, then you should err on the side of caution and make up whatever you think most likely to be the number of prayers so that you will have discharged your obligation.
For more information, please see the answers to questions no.  42574 and 101605.
And Allah knows best.