Make sure some of your filter material is seeded and keep a very close eye on water parameters. You may need to do daily WCs to keep things in check. Also what are you feeding the fish?
What is generally thought of as HITH is primarily caused from nutrient deficiency and poor water quality. The addition of Omega 3s and Vitamin C is shown to help improve the condition in combination to diet improvement. Selcon is an excellent food soak for this purpose. Now it is also possible that what your fish has is caused by the Hexamita parasite...to general human observation distinguishing the two is really not accurate as symptoms mimic and is usually a process of elimination. For the sake of the fish I would also treat for Hexamita. Do a combination treatment of PraziPro and Metro+. If the fish is still feeding use the Metro+ as a food soak...it is very effective used internally.
Also if you just recently moved the fish lying on its side is a common Oscar thing known as "sulking".
150G SA Cichlids|100G Planted Community|50G Reef|20G Tanganyikan|10G Divided Bettas|10G Nano Fish
Common decency...imagine the nerve!