This is probably a pinguecula - a very common type of conjunctival degeneration which looks like a raised yellow/white deposit on the white of your eye nearest the nose.

It's not usually painful, but it can be uncomfortable. If so, it's best to use lubricating eye drops to help, and possibly antihistamine eye drops as the allergy may cause more irritation. Pinguecula rarely need any treatment but can be removed or helped with steroid eye drops, for which you need to see an eye specialist.

If it's painful, you may have an eye infection like conjunctivitis or the pinguecula itself may be infected and need medication - in this case, it's best to see your optician or GP as soon as possible.