AD620 simulation Problem
Ref ought to be tied to some voltage between the two power rails and you have an input open circuit, Example here: -



You will also find that the way you have pin 2 connected is illegal. Pin 2 fails to be a reliable input when it gets closer than 1.9 volts to the negative rail (pin 4) or ground in your circuit.

An input is amplified between pins 2 and pin 3 - I don't know where pin 3 is suppoed to be but pin 2 is at an illegal voltage (ground).

Also, using a pot to set a gain of 5000 is nonesence - the gain equation requires Rg to be about 10 ohms and a 20k pot will be as noisy as hell when trying to get the wiper ten ohms away from one end of the range - use a fixed resistor and take into account temperature drift (if necessary).

When you do get the inputs, Rg and pin 5 sorted out don't expect miracles from the output when powered on a 5V rail on ground. The DS specifies that the output can range from -Vs + 1.1V to +Vs - 1.2V and for a 5V supply that means you can rely ONLY on the output when it is between 1.1 volts and 3.8 volts.


  I have calculated the value of the resistance as 0.0101194 ohms


Gain = 1 + 49k/Rg so clearly Rg approximately equals 10 ohms.