Maybe you should do a follow up with your doctor to make sure the parasite is gone. If it is, they might be able to do further tests. The preparation h shouldn't do anything because it wouldn't increase your digestion time. It would more likely effect what comes out and not when. I don't see that the alcohol would be cause for anything either (although a glass of wine makes me run to the bathroom, but only right after I drink it)

Perhaps it's something you are eating. It is possible to become intolerant to a food that never caused you trouble in the past, I recently discovered that i'm lactose intolerant and I used to stomach dairy products normally until recently.

You could be suffering from irritable bowel syndrome or simply amoebiasis. The characteristic few symptoms are urge for stool after eating, urge for stool with urgency, infeffectual urge for stool, loose stool, mucus filled in stool sometimes etc.
Homeopathic medicine has good remedies like nux vom, sulph, merc, lycopodium, kurchi etc. Which help in getting rid of the problem.
Dr.Venugopal gouri.

If it happens after sweets or sugary foods--it could be "dumping syndrome"

when your intestine gets a big load of sugar, it can cause you to have to poop right away--you can help it by having some fiber or fat with your meal to slow things down a bit or just avoid processed carbs like white flour and sugar

also the fake sugars like maltitol and stuff are major diarrhea producers

it is probably dietary, sometimes you can elimiate certain food groups--like dairy or nuts, etc for a few days and see if that clears it up

i get the runs anytime I have a lot of fiber, if it has been a long time since I had any, I have to build up my tolerance for it...
Some peoples' tummies are more sensitive thanothers...

Also, I used to be able to eat whatever, I never got sick, but now in my old age I have to take it easier

also, if you are on a new medication like effexor or zoloft--it can speed up your intestine motility...