As some others have eluded to, I think the OP will in for a shock with his “3 month crash course” plan. Learning & mastering another trade to the point where you are matching your take home earnings as a Class 1 driver can often take years. Go for it by all means, but you might have to adjust your lifestyle in order to afford it in the short term.
I’ve got another career in mind right now, the stumbling block is the £13,500 cost of the course. That’ll take 18 months to complete part time and I’d still be dropping some money initially.
If your only background is driving, one option is to try the office route to try & gain some transferable skills such as IT/people management etc.