It may be a weird comparison but remember when everybody thought the world was flat and it was basically a common known fact and yadda ya, it's all everybody knew and it could be the same about your prophet. Abraham kept concubines and its a known fact that concubines in that time were young male boys. But they didn't know any better...
For me as a Christian, there are LOADS of rules and commandments and ideals that I should follow but my personal beliefs that I have gained as a 'westerner'/Briton counteract with that. There are a lot of denominations which are just as 'strict' as islam too.
It's good though that you're questioning your religion because that's where faith grows stronger. Many of God's closest servants did it in the Bible outright telling God they're opinion and that he was wrong xD
Also read your Holy Book because maybe there is a reason why in context.
eg The Bible says we aren't to have tattoos but when you read I think Leviticus you get a better understanding of why it was relevant THEN (it was because the gentiles and pagans marked their skin and as israelites God wanted his chosen people to be distinguished from non believers)
At the end of the day, it has to be a relationship between you and God not you and everybody else goverened by these rules.