Clive I suspect you're seeing a combination of things, mostly already mentioned by others.
1) Strava seems to massively overestimate running calorie expenditure compared to any other means of estimation (weight/distance/time, heart rate etc). A typical 5 mile run for me would be around 500-550 calories by most calculations, but Strava displays 650-700 for the same activity. Even though it has my weight saved and should know better.
2) The comments about food diaries and weighing your food are all valid - I did that for over a year although don't any more. In your case though it's highly unlikely that you have put on 6lbs of fat in two weeks. You'd be looking at ~21000 calories or around 200 miles as per Literatin's post. You'd have to be doing some pretty drastic consumption to manage that without feeling sick.
3) However it's much easier to put on 6lb of glycogen+water weight in that time. Especially if you weren't eating loads all along then you limited your exercise, as your before and after measurements may be comparing an empty glycogen 'tank' to a full glycogen tank. It's even easier to put on more water weight if you've recently been drinking alcohol or eating salty foods. If you haven't had a good clear out recently then you may also be including more weight of goods 'in transit' that you realise.
Also, depending upon where you're travelling to, and whether you have an unlocked smartphone available, it might be worth buying a prepay SIM for that country, or stick £10-£20 on a GiffGaff SIM - the EU data roaming charges at least aren't too bad nowadays.
Most phone running apps will still work without a data connection as the actual tracking relies on the GPS chip not the cellular data. Expect to lose some features that rely on the data connection like maps and live web-based tracking, but expect the app to work for time, distance, pace and recording co-ordinates that you will be able to see on a map once you do eventually get back to wifi or home to a data connection.