Hey man -
I've dealt with some sciatica stuff over the years as well as varying injuries and just wanted to throw in my $.02.
I would say it is almost a certainty that your issues are from aggravation in your lower back due mainly to your lifting form while lifting heavy. If there's NO way you are going to cut out heavy lifting (which I definitely understand as I love lifting heavy) I highly recommend that you start doing jefferson curls, as well as incorporate a serious stretching and flexibility routing. J curls are the single best exercise for stretching out our lower back and spine. You can do your own research or PM me for more info if you're interested, but once you incorporate jefferson curls into your routine there's no reason you can't squat, DL, etc.
I also recommend this interview to ANY person who plans on being physical for the rest of their lives. Tim Ferris kind of tilts me but Christopher Sommers is on a whole different level when it comes to body knowledge:
https://www.youtube.com/watch?v=EzyAPEWOlxw
Basically flexibility and posture are the nuts for long term physical health.
I made the extremely difficult decision to effectively retire from jiu jitsu after taking full inventory of what I want in my life, and looking at the problems caused from it in my friends and coaches. I also started to have this weird lower back thing, right on my sciatic nerve (and associated numbness and nerve "jolts"), that has completely disappeared after stopping bjj.
Now I am as built/ripped as I've ever been, and all I do is a lifting/flexibilty/yoga/gymnastic regiment, and I swim 3x a week. I find the feeling of having "real strength" and flexibility way more satisfying than I ever felt from the heavy lifting I did.
Anyways I know that's probably a bunch of stuff you don't want or care to hear, but hopefully something I said can help you at some point along your journey. GL!