Why is my 3g not working well?

My 3g signal is weak most places, but inside stores and big buildings I have no 3g and cannot even send texts. I have taken my phone apart numerous amounts of times. I am not sure if something is installed incorrectly. All metal on metal connections are degreased.

Also, my rear camera is not working but the front camera is. Does the back camera just need to be replaced?

Thank you!