Diode current voltage characteristic issues

I'm trying to find current-voltage characteristic of a red LED diode in the biggest possible range using 5 3 V batteries, 1 100 Ω resistor and 10 diodes, but my graph is wrong

The measurement is taken using two voltmeters one connected parallel to the diode to measure its voltage drop and one connected parallel to the resistor to measure the current in the circuit.Is it because I'm using too big of a voltage for one diode that the graph becomes linear after 5 V on the diode? The current also seems off.I have to use only the equipment I listed.

Edit:

Here's a picture of the circuit

and of the diode

I varied the voltage by adding/ removing diodes and number of batteries.