trying to plan summer vacations

Rebecca
So I am 5 weeks and 1 day today. I am due in late august early September and the only ones that know is myself and my husband. We don't want to tell anyone I the family until the first ultrasound and until the doctor says I am in the clear and good to tell others. HOWEVER my family is trying to plan flights and trips in JULY ! And it's difficult to keep it from them that I may not be able to fly then and won't be able to do any trips. 
Have you guys dealt with this before ?!? How do you handle something like this until you make the big announcement ?! 
BTW I cannot wait to tell them all so it's very difficult to keep it from them!!!