Flaccid erection of penis after Appendix surgery is just a coincidence.It is not related to surgery at all.Again urinary streamidoes not depend on stiffness
of penis as it is Urethra through which Urine is expelled.Whatever you are suspecting is wrong . Erection is all together different complex mechanism that involves Central nervous system
,Vascular system in Penis and Psychology It is better if you consult urologist
for your problem.but i think it is psychological and there is an element of Anxity rather than any organic cause.