I'm guessing that you've experienced some damage over the course of your 13 year usage, even if you're doing a good job with rotation of sites and hygiene. Methamphetamine is pretty caustic to soft tissue relative to say, Heroin. I've known Methamphetamine users to slowly damage their larger veins, move to tributary veins like hand or forearm and then begin to experience symptoms like what you're describing as these veins become damaged. My understanding has always been that the drug is likely "leaking" out of these smaller, frailer veins and causing pain like you're describing.
I wish I had better news for you. I'm not aware of a practical means of restoring your veins. A lot of you who know me know my story with injection. I injected Heroin for a decade and had little to no damage. I would still regularly rotate from 4 primary sites, crook of elbow and one of the veins on the close side of either arm. After years of success, I got the bright idea to inject my take-home Methadone ~4 times. I completely destroyed almost all of the usable veins in my arms. It was absolutely horrible. I am years and years on from this now and on bad days, I still need the ultrasound machine to get a vein when I need blood taken.
My understanding is that it is possible for us to "create" new veins to replace damaged ones, though these "new" veins are often extremely small/fragile. It's good news that there is a means of replenishment for our bodies, though this doesn't help someone who is trying to inject. I would at least consider a different route of administration. This problem is likely only going to get worse.