Can only feel prostrate while stroking penis

Everyone says not to touch your dick so much and avoid masturbating the usual way. But when I have my Syn in there I can’t really feel much even contracting unless I also stroke my dick.

While I’m stroking I can suddenly feel my prostrate swell and touch the toy, which feels just a little nice (I’m not at a stage where it’s amazing or anything). Just a second or two after I let go of my dick I think my prostrate just sort of retracts back and I can’t feel anything down there any more. What do I do?