Does anyone know what this is on my fish?

Could you put up some more pictures and are you talking about the white dots. If so then it is most likely ich. There are ich treatments you can order online or buy in your local fish store. You can also raise the temperature in the tank but I would research that because I’m not sure for how long.

Need pictures from both sides but I'm going with hole in the head disease caused by hexamita, which is normally caused by a dirty environment.

--------------------

BASIC FIRST AID FOR FISH
Test the water for ammonia, nitrite, nitrate and pH. Post the results in numbers here.

Wipe the inside of the glass down with a clean fish sponge. This removes the biofilm on the glass and the biofilm will contain lots of harmful bacteria, fungus, protozoans and various other microscopic life forms.

Do a 75% water change and gravel clean the substrate every day for a week. The water changes and gravel cleaning will reduce the number of disease organisms in the water and provide a cleaner environment for the fish to recover in. It also removes a lot of the gunk and this means any medication can work on treating the fish instead of being wasted killing the pathogens in the gunk.
Make sure any new water is free of chlorine/ chloramine before it is added to the tank.

Clean the filter if it hasn't been done in the last 2 weeks. However, if the filter is less than 6 weeks old, do not clean it. Wash the filter materials/ media in a bucket of tank water and re-use the media. Tip the bucket of dirty water on the garden/ lawn. Cleaning the filter means less gunk and cleaner water with fewer pathogens so any medication (if needed) will work more effectively on the fish.

Increase surface turbulence/ aeration to maximise the dissolved oxygen in the water.

See how it looks in a week. You might need to treat it with salt or Metronidazole. But do water changes and gravel cleans for a week and then post more pictures before looking for medications.

Looks like hole in the head to me as well

If it is Hexamita, I would know exactly how to treat it. But I am in the states and we can get a lot of meds here that are not available in other countries. I have the med. below as one of those I always have in my fish medicine box.
Flubendazole-Effective treatment for Hydra, Intestinal Parasites including Hexamita, Gill Flukes and Camallanus
https://www.inkmkr.com/Fish/FlubendazoleTreatment.pdf

The OP is in the UK and we can buy flubendazole here. It's the active ingredient in N T Labs Anti Fluke & Wormer, and Maidenhead Aquatics own brand AquaCare Anti Fluke & Wormer.

If it is hexamita, then early stages can normally be treated with clean water and salt. In more advanced cases metronidazole is required or something that treats hexamita.

SALT
You can add rock salt (often sold as aquarium salt), swimming pool salt, or any non iodised salt (sodium chloride) to the aquarium at the dose rate of 1 heaped tablespoon per 20 litres of water. If there is no improvement after 48 hours you can double that dose rate so there is 2 heaped tablespoons of salt per 20 litres.

Keep the salt level like this for at least 2 weeks but no longer than 4 weeks otherwise kidney damage can occur. Kidney damage is more likely to occur in fish from soft water (tetras, Corydoras, angelfish, Bettas & gouramis, loaches) that are exposed to high levels of salt for an extended period of time, and is not an issue with livebearers, rainbowfish or other salt tolerant species.

The salt will not affect the beneficial filter bacteria, fish, plants, shrimp or snails.

After you use salt and the fish have recovered, you do a 10% water change each day for a week using only fresh water that has been dechlorinated. Then do a 20% water change each day for a week. Then you can do bigger water changes after that. This dilutes the salt out of the tank slowly so it doesn't harm the fish.

If you do water changes while using salt, you need to treat the new water with salt before adding it to the tank. This will keep the salt level stable in the tank and minimise stress on the fish.

When you first add salt, add the salt to a small bucket of tank water and dissolve the salt. Then slowly pour the salt water into the tank near the filter outlet. Add the salt over a couple of minutes.