I'm getting a blister from my ring?!

Yup that's what I was going to say. Get it rhodium plated (it's pure platinum. No nickel) and it will go away. When it starts to come back, get it dipped in the rhodium again

Time for a new ring. You have an allergy I bet.

I was told it could possibly be due to the pattern on the inside of the ring?

I'd call that an allergy. It's exactly what it looks like if I wear jewelry with nickel on it. I don't think it's the shape of the underside, just the metal

I'm much more likely to try getting it coated than I am to replace it. We spent a year in Australia together, got the ring there, and he proposed on our last night in the country. There is a lot of sentimental value to my rings beyond just getting enagaged/married

So the underside of my band looks like yours, OP, and when I first started wearing mine, I blistered and then the skin cracked and it was in the same shape as the band. I took it to a jeweler to get cleaned and the jeweler said it was because I likely used bleach, spic n span, Clorox, or something similar while cleaning and because I didn't wash my hands thoroughly/remove my ring while cleaning, my skin broke out and had chemical burns under my ring. So, I would get it professionally cleaned, dipped, and leave it off until your hand heals. Then keep it clean. They gave me some kind of green liquid solution to leave my ring in for a couple hours each night in between professional cleanings to prevent another chemical burn (but I also take my ring off now when I clean!)

ETA: I also am highly allergic to both copper and nickel. I can't even have loose change in my pocket because my thigh will break out into hives, can't wear a silver plated belt because when it wears off the copper will send me into hives, etc., so I also agree with PPs about the fact that it could be made with nickel or copper. You can have it plated as they said, but in my experience, it could wear off. Maybe not. I would personally think about investing in a less mixed-metal band to prevent a serious reaction. The longer you wear it in the condition it's in, the worse that reaction will be.

UPDATE: I have friends who say they've had this sort of situation. They were told by professionals it was soap scum buildup, so they cleaned it up and it went away. I'm going to try this first, and if it doesn't go away, I'll either get it dipped or see a dermatologist for a professional opinion

I used to get that with my first marriage engagement ring when I would wash my hands with my ring on and water would get trapped under the ring. The ring also was not smooth on the inside which made it rub and would give me the issue. Once I started taking the ring off to wash my hands it solved the issue.

I'm having the same problem but it's in the space between my fingers. I was thinking it could be my ring guard and was thinking of having it sized. Based on the comments I will do that and also have it dipped

JNav, my one friend told me she cleaned her ring with Hydrogen Peroxide and Boiling Water to clear up the soap scum. That's what I'm going to try first (after I research it to make sure it won't damage my ring). Then I'll make sure I take the ring off when I wash my hands and see if it clears up.

Looks to small to me.

That's what happens to me when I wear jewerly. I have nickel allergy. Can only wear 14k yellow gold. White gold makes me break out.