Sometimes, Photoshop stops picking up pen pressure. When that happens, the following might help.
Open the following folder (or whatever version):
C:\Users\[User]\AppData\Roaming\Adobe\Adobe Photoshop CC 2015\Adobe Photoshop CC 2015 Settings\
If the file "PSUserConfig.txt" already exists, rename or remove it.
Start Photoshop and close it again.
Create a new file named "PSUserConfig.txt".
Open the file and insert the following text: