Trouble getting pregnant

Brittany👨‍👩‍👦‍👦☕️ • 28 yr old Boymom of two wonderful boys, Blaine and August. Currently pregnant with #3! Due December 2016 😍
I have a very good friend who has been ttc for years. When I found out I was pregnant she told me she was to but ended up having a miscarriage. Well about two weeks ago she told me she's pregnant again but her HCG levels are low. Of course I'm super excited for her!! She had a dr appt today and she's measuring 2 weeks behind..5 wks instead of 7wks. I've never had a problem getting pregnant or being pregnant so I don't know anything about HCG levels or the measuring behind but is being that much behind ok? I'm currently 4 days away from having my baby boy and every time I talk to her I feel bad. She's never been negative towards me about being pregnant which is amazing but I'm sure it's not easy for her. I guess I'm just looking for other stories like hers. She has another appt next week and hopefully they'll hear a heartbeat!