Is there any reliable sources for the history of the middle ages?

Of course there are. Cambridge University has published a whole series of history books about every epoch, and Oxford University has done the same.
I have a few favorites: A Distant Mirror: The Calamitous 14th Century by Barbara Tuchman is an award winning examination of the crises of the 14th century, and some of the narrative is gripping. She's a gifted writer.
I also enjoy the writings of a French couple, Frances and Joseph Gies. Their books are about daily life and titles include Life in a Medieval Village, Cathedral, Forge and Waterwheel, Women in the Middle Ages and Life in a Medieval Castle. Civilization of the Middle Ages by Norman E.Cantor is a classic.