With Manchester United ive had the first half of the season's fixtures exactly the same as the second half only its the return fixture. Ive also had Arsnal, liverpool, chelsea, city back to back.

How do i change this? Its way too unrealistic.

Its not that unrealistic. Portsmouth had Man U (h), Bolton (h), Chelsea (a), Arsenal (a) and Liverpool (h). All of the top 4 in the space of 5 games.

You can't change it - unless you start a new game - or revert to a save before the fixtures were announced.

Go and have a look, most leagues do have the second half as the same as the first half, with only a few changes due to clashes with cups etc...its not too unrealistic, as for the big teams in a row, there has to be one team with a bad draw, this season it is just your turn.

most leagues have the same order of games, but i'vr noticed ive had similar fixtures for a couple of seasons in a row. will have to wait and see what happens in the next season to see if its coincindence or actually a bug/programmed that way

Actually, in the Premier League, the fixture list is random, so yes, what the OP is experiencing is very unrealistic.