I sometimes have clear penile discharge when straining during a bowel movement, is this normal?

Clear OK. It is likely from the bm pushing against your prostate on its way out and is normal. If changes color / volume / odor or becomes painful, then be concerned.
Prostate Fluid. This is common. It is prostate fluid, semen and sperm.

Related Questions

Recently I have experienced white liquid discharge from penis during bowel movements. I am quite worried about that. Is it normal?

No. This is not normal it could be several things even it could be a tract tunneling from your intestine to the urethra tube in your penis. Consult a urologist in person for diagnosis and treatment.