Well try and not beat yourself up too much and just take it as easy as possible. Does the gabapentin and seroquel help you out at all? I'm sure there's a legitimate reason you take it if a doctor prescribed it.
Have you ever considered inpatient rehab, or at a minimum AA/NA meetings? If your use is becoming very problematic you might want to consider looking into one of those. Those are options, and then there's also medication maintenance which is one way to taper off of drugs. If you're trying to quit meth, it might be easier to just stop it outright and just get through the withdrawal. Stimulant withdrawal can suck, and it has physical components, but it is still mostly mental.