For instance I'm giving it 1.5 volts and the readings from the pin are jumping from 20 up to 153 and back down.
Those numbers are not consistent with the value you should see: 1.5/5 * 1023 = 307. It looks like something is not properly connected.
Can you provide some information on the pressure sensors, and how you have them connected to the arduino and power?
Is the arduino ground connected to the sensor ground?