anxiety problems... help please?

Im a 15 year old girl and I get this weird strong anxiety feeling whenever my parents go on vacation... its so weird but I get such bad anxiety... my aunt is staying with me and I love her so much she is the funniest person ever so she isnt the problem.. im not worried about something happen to them but I cant seem to shake this awful feeling.. they are leaving next weeknfor a week and im freaking out...I dont get anxiety attacks but its a very strong feeling that I cant stand.. is there any over the counter medications I can get or anything that can help... this is a big important issue for me so any ideas you may have I would love to try