Hi Hellya,
Yes, it is so that that DAW plugins generally aren't for mastering with, but then I would argue that isn't really the issue here, it's what the song needs, the type of PI you choose and how much control they give you over your content. Depending on how good your mixes are, you could get way with just a simple stereo buss compressor. However, you defo want to get a 3 or 4 band multiband compressor and a really precise multiband EQ (A multiband comp can also be used like a multiband EQ). Don't forget, Producer versions also have the linear-phase LP-64 EQ and multiband compressors.
A couple of chains might be
e.g. buss compressor > EQ > Limiter > Reverb or
buss compressor > EQ > Multiband compressor > > Widener > >Exciter > Limiter > Reverb
And - to get a more analog/vintage sound you might add a unit offering a degree of distortion and high end roll-off somewhere in the mastering chain such as the TL-64 Tube Leveler or even the Blue Tubes Analog TrackBox or ProChannel Tape simulator. Also have a look around for free PIns.
Here's a nice intro to setting up a basic mastering chain:
http://www.musicradar.com...ain-in-your-daw-601562 Grab this for a comprehensive overview
http://downloads.izotope....MasteringWithOzone.pdf So - listen to the mix first, decide what processing it needs and then choose the units. Remember, there are no rules, just guidelines.
One last thing - it's hard to mix your own music but if you do, take a few days, even a weeks break from those tracks to rest your ears and get them out of your head! It'll help to make you more objective. Try to take a lot of breaks. Mastering is about adding polish, not fixing - any problems need to be sorted out back in the mix. It shouldn't take more than an hour to master each song - any longer then you need to stop and rest and think about why it's not working.
Not sure if this answers your question properly but I hope it helps - all the best with it!
Gary