One of the contradictions about academic writing is that while you are expected to read, research and refer to experts and authorities, you are also expected to produce 'original' work.
So, you are asked for your view, but it must also contain academic research. Therefore, you plagiarise because you're not sure how to develop your own argument, or don't have the confidence in your conclusions.
You need to realise the ways in which your own ideas (your voice) may be incorporated into your own writing.
Most of the work you will do at uni will concern the words, information and ideas of other writers and researchers. When writing assignments, your job is to synthesise answers from the opinions of others, rather than just think up an answer 'off the top of your own head'.
Don't be concerned about drawing from various sources. Student writers, especially early on, are more like DJs 'sampling' than classical composers. Even if you are writing a PhD, you still need to develop your ideas in relation to other writers.
Finding your own voice is not about saying something original (something that no other person has ever said before) but about producing something of your own from the ideas/ research in the same way in which DJs produce 'original' music from the pre-recorded sounds of other music 'writers'.