Pls help!

I have a common pleco which was 1 inch when I got last September. Now its close to 8 inches, he has bog wood, & his daily diet is alternate cucumber & zucchini with tablets or wafer. He does'nt like leafy vegetables. He eats very well, he can consume the whole cucumber or zuchinni in a night. He has very good appetite.
My problem lately is i suspect he has intestinal blockage or i think that what it is because suddenly he stop eating cucumber or zuchinni for 3 days now which very unlikely of him, he is lethargic and his tummy is big or he is just fat. He is fat because his eyes is protruding out.
i did not see his stool this past few days. I made a big mistake of putting small artificial plants recently which i think he ate them. I put it for small fishes as the real plants i put is almost gone, pleco eats it. I pulled all the artificial plants out of the tank. What can i do to save him??? please help any suggestions?? or
Is there any reason that he may have change his diet??? because, I could not find my baby mollies. They were 10, then it became 9, then 7, then two days ago it became 4. I have other small fish like 5 glass fish & 1 betta with 3 grown mollies (2female, 1 male)for a long time he never bother them since the beginning. I am confused... Is he going to die??? I put every night cucumber & tablet but he don't touch them anymore?? :help: but he ate the small fish....is there any cure for intestinal blockage????

tank is 55 gal. Sorry my plec is now over 8 inches. I never check the water parameter bec. i changed the water every weekend, although sometimes twice a week until the water is clear because there are times the water becomes cloudy. 20% change of water or sometimes more than that. I have canister filter. I dont check the water temp. either because it is hot now in Cyprus. It's summer here goes up to 40 C out side.
This is an abrupt change in the behavior of my plec. He is not as active as before and my concern now is he doesn't eat. & doesn't pooh. He is also friendly to other small fish, never bother them. I always make a point that he is stuff up at night so he will not get hungry to bother the small fish and this happens. I feed all the fish once, & this is at around 7 pm. I feed the others with frozen blood worms & flakes. For plec is either zucchini or cucumber plus tablets.
I'm wondering about the disappearance of the baby fish. They were bred from the grown mollies this last February. The size of baby fish is more than half inch now & disappear some the following mornings. I didn't see any bodies. The plec never bother them just until now what i suspect, my plec is the culprit. Im really confused...

what are the symptoms if its parasite?? where it came from?? I'm using ocean nutrition frozen blood worms. Never had any problems with other small fish, they are eating well and no signs of lesions or any wierd behavior except for the big plec.
What shall i do if it's parasitic??? or intestinal blockage??? will he survive?? im really worried about this fish.:headshake2:

ill have to look for liquid test kit. would you recommend any brand????

if its intestinal blockage, which i think, does anyone knows if there's any chance for him to recover???
he stop scraping even his wood, & the glass.