You're not the only one. But you can get over it, and must, really.
Several options:
Take an experienced friend along. Work your way up from major A-roads, so that you can carry the confidence you feel with your df on those roads along with you as you progress to a motorway.
Book some motorway driving lessons (IMO they should be obligatory).
Get some confidence-building, trauma-recovery hypnotherapy.
BTW the first time I drove on a motorway I hyperventilated so badly that my vision was affected. I never liked motorway driving, but did it anyway - mostly in the lh lane! And about 5y ago I had a near-miss on the M4. It was terrifying, but I had to continue driving. And, what's more, I had to drive home that night, in the dark. I was nauseated with nerves, but, again, I did it. It took me months to get over the fear that the near miss left me, but I had to drive. Now I use the motorway, all 3 lanes, with some muttering, but no nerves.