Double stop pain
I took a multiple decade break from violin and got back into it a year ago. Now that I'm big, I can't play double stops (example: Hungarian Rhapsody no 1) without a lot of hand pain going from 2/4th finger to 1/3rd fingers. Any recommendations? I tried lowering my shoulder rest to give me more room to bring my fingers over, but it's still uncomfortable.
Do you have a teacher? If not, it might be a good idea to get one to help you get back your technique after such a long break. I took a 25-year hiatus and immediately got a teacher, which helped me immensely. That way, you have someone who can watch your technique and help you restore it and improve it. Anyhow, a teacher can watch how you do the double stops and figure out what you need to change so that you are not in pain. It is also possible that you tried to do something to difficult too soon after restarting and strained something. Good luck!
There could be a number of causes for this pain:
After such a long break, it is a bit too optimistic to jump into double stops after only 1 year. "Multiple decades" translates into that you are not such a young person anymore, so you need to be very careful if you want to avoid injuries and enjoy playing as long as you live. Your love for music, your feelings are not at the same level as your tendons, joints, nerves and the rest of the body.
Is what you are trying parallel thirds 1-3 and 2-4 ? Thirds are especially difficult because of the physical awkwardness and the difficulty of tuning. Try lifting the fingers you are not using instead of leaving them down. The 3rd and 4th fingers are not completely independent, they share a tendon somewhere. Pianists are more aware this problem than violinists.
Threre is one thing I don't understand: You say "now that I'm big": Does that mean you were small when you abandoned the instrument? Or why else do you say that?
I infer that the OP feels his larger size compared to his youthful size is the main reason he's struggling with parallel thirds. This is likely to be among the least of his problems.
I would go slow with the double stops. It's easy to press too much, and you want your fingers to make contact as lightly as possible. A vice-grip is going to come back to bite you. Slow scales is a good idea, as Paul points out.
Double-stops and chords require a firmer stop than single notes, for clarity.