I cannot see anything in those 3 photos that would make me panick about the health of the catfish.
I'm not going to try and identify which species this catfish is, but I can tell you I'm pretty confident it is not a "Bulldog" (Chaetostoma spp.) Pleco. I think you should post these same photos in a thread at PlanetCatfish in the
http
/www.planetcatfish.com/forum/viewforum.php?f=13 section, to get the opinion of members including professional ichthyologists.
At the very least this will identify the genus so you will get a better idea of the food requirements of this fish, some need soft wood in their tank; others are mixed omnivores; others need a heavily biased veg/meat diet.
If you have been doing at least 15% (but ideally a lot closer to 50%) weekly water changes, I would still be inclined to do a 75-95% water change, to ensure water quality is not stressing the plec. Put aside a little of the current water to test when possible, but you really should get your own liquid test kit ASAP.
On a sidenote, relatively few Malawi cichlids are suitable for a Juwel Trigon 190 long term, you would have far more options from Lake Tanganyika. Both require very hard alkaline water and as such, you need to be able to test their water quickly, because such water at ~25C will be toxic at relatively low levels of ammonia or nitrite.