1.14 is totally appopriate for the metal riffs that you are playing.
Infact anythign thinner would require more effort from your part.
First thing first: I am assuming you are talking about index fringer of your plectrum hand. (wanted to make this clear because most humans have two index fingers)
Second thing: your finger is paining because you are making your fingers too tense. That means either your picking style is not correct, or your pick holding style is not comfortable, or simple that you need to slow down your picking and let your body adjust slowly.
You should also mention where exacly in/on your index finger do you get the pain.
You donít get what you deserve, you get what you negotiate.