Mobile heats up alot, low signals issue after changing body iPhone 5s

iPhone 5s 64 GB

I replaced the body of my iphone with the help of ifixit.com

But after that my mobile heats up a lot (while charging, playing a game or using 4G) and the battery time of my mobile is so bad, no standby time at all. In 8 hours my fully charged mobile is dead.

The second issue is im getting low signals of my carrier and as well of my wifi i used to get full signals in my room of my carrier and wifi and now (3-4 signals of carrier and 2 signals of wifi) is there any solution of that? Or it'll stay this way forever?