Forgive me if there is somewhat of a language problem, but do you mean by "electric shower" that the water is heated electrically? Additionally, if the shower wather control is a single lever and relatively new, it should be an "anti-scald" type to assure hot-cold balance. The pressure balance mechanism that does this could be failing, however unlikely.
Are you in an apartment complex or a single family dwelling. Other water users in apartments can also affect water pressure causing your discomfort...