Hi hon, it does sound like he is sleeping a lot during the day for a 6mth old - but don't worry he's not a problem child, just one getting used to weaning and sleep patterns.
I would gradually try and get him into a better routine and cut out the 3pm nap - it's too late. To improve the bf, try feeding him after food and before a nap - but not after it. One morning nap and 1 afternoon nap should be plenty, and will improve his sleeping at night.
From memory at 6 mths my first lo was having lunch around 12 and then a good 2 hr nap straight after. He would then not sleep again till 7pm bedtime. In the morning he would wake about 6-7 and then come into my bed for a bf and sleep till about 8 or 9am.
You need to improve his routine gradually, it won't happen overnight. I read that you can adjust nap times by 15 mins per day and they will soon learn!
As for the crying, well that's totally normal! Some girls are lucky and have babies that are q happy to be left, but my first was a nightmare, v demanding and I barely had time to take a shower without him crying! It does get better though!
Hope this helps a bit, sorry I can't be more help but just remember he's still very little and it will take time.
xx