When I stretched my lobes to a 6g, it was difficult as well. I tried several different times over the period of about a week before it finally worked. I'm sure it's the most difficult so far because of the size jump. For me, it wasn't at all like my previous stretches. I know people who made the jump super easily, and people who found it really hard.
Metal: 4g lobes, 18g right nostril, 16g(?) tragus, full set of braces
Upcoming: 2nd lobes, conch, several more
Retired: first set of 20g lobes forever ago, 16g second lobes, right ear industrial, left nostril, 14g navel (Obviously piercings don't love to stay in my body happily.)