I'm no expert, but when i've had infections, i can usually smell them without needing to physically lift my underwear up to my nose. When i'm infection free i can only smell a very slight scent if i actually "try" to smell any discharge by bringing it up to my nose area to check whether in my opinion it smells "healthy". Everybody is different and some people will have a discharge with a stronger odour which wont necessarily mean they have an infection. They may also experience more discharge as they get closer to their period and i always think the more discharge the more chance of an actual scent.

If the odour does change to something questionable, i always visit my doctor for him to do a culture of the vaginal mucous.

Appart from my doctor, my husband is good at telling me whether alls well as he'll normally say things smell great down there with a big smile on his face :D Women can become very paranoid about scents around the vaginal area, thinking there shouldn't be any scent at all, when in fact everybody has some form of scent. I've never really taken so much notice about varying times of the cycle, appart from noticing more discharge before my period.