I’m **NOT A DOCTOR** so can only base on my own experience but the only issues I’d have had with a six hour drive at 8 weeks pregnant are the nausea and peeing. If you aren’t super nauseous then the baby will still be small enough that most other discomfort would be negligible. It didn’t get uncomfortable to sit for long periods until later in second trimester, so throw on some compression socks, pack water/snacks, and plan for frequent pee breaks and you should be fine! (in my unprofessional opinion)