Lubricant isn't going to make any difference if you are having sex with a steady partner or not. You can get rubbed and sore from not using it.
You are only 16, so I'm going to suggest that you hold off the sex until you are actually ready, because it doesn't look like you are....it disturbs me that you are so ignorant about your own body, not to mention sex. Also sleeping with random and multiple people is dangerous. You are at risk for STDs and if you become pregnant you would have more than a load of problems.
That being said, your vagina is probably not going to grow considerably more to make a difference. The vagina is very elastic and can accommodate a baby's head passing though it and can hold in a tampon. So getting things in isn't the problem with the size of your vagina.