Vaginal dryness?

Hey guys i'm a 19 year old male and my girlfriend is 19 as well. We recently started having sex. We've been dating for about 6 months and we've had sex quite a bit. During sex I last between 45minutes to an hour. I've never been able to *** early for some reason. When we have sex the first 30 minutes are great but after about 30 her vagina starts to slowly become "dry" its painful for her and sometimes a bit irritating to me. Google said it could be her getting "turned off" but she swears up and down that isn't the case. She says she feels like after 30-35 mins of sex her body starts to get tired. Is this normal? Should I spend more time on fore play. We usually make out for about 10 minutes then I finger/ eat her out for another 10 and then we have sex. Should I just buy lube? Or should I spend more time on foreplay Please help!!!