Centre brake light works but no outside lights

Hello,
From your very brief description I would purchase two replacement bulbs for the lights that aren't working, although you may have looked at them and they seem o.k. the filiaments on the brake light side are heavier than sidelight ones so if fused sometimes you can't see the break in them.
As your third brakelight is fully functional this is the reason I would be looking for replacement.
I hope this helps? please remember to appraise my FREE effort and press that Blue button if sorted, Thank You!
Paul 'W' U.K.