What you are describing is common for night work. Your decision to maintain the same sleep schedule on your off days as your work days is the best thing you can do. Still, you are awake when it is dark, and asleep when it is daylight. Your body hates this, and is rebelling with headaches.
Even regular day workers who make a habit of staying up late on Friday and Saturday and sleeping late the following mornings get in trouble. If you have heard of "sleep hygiene" this is what it talks about. Do searches on sleep hygiene, and you may find some useful info.
I can partially relate because I was a pizza driver 25 years ago. I typically got home at 3:00AM, so I tried to keep the same schedule. I was in college, so I never took any classes that started before 10:15, and I usually took afternoon and evening classes.
One other thing. Get blackout curtains for your bedroom when you are day sleeping. Another trick is to get the cheap aluminum oven-sized trays and spray-painting them white to put in your windows. Avoid seeing ANY sunshine because the wavelengths the sun emits trigger reactions in your body to wake you up and hinder sleep.
Getting up to go to the bathroom can be a problem depending on your home's layout, but dark sunglasses that block side light can help a good bit.
I hope this helps...
Run a fan to drown out noises, and consider ear plugs.