I bought an annual plan with STA Travel, but they require you to have been in the country for 3 months, I believe. They also have plans that US residents can buy online, but I am not sure if you would qualify for that since, technically, they would view your 'trip' as having already started, since you are outside of the US currently. When I bought my plan, they used the day I left the country as the policy start date. It might be worth looking into, at any rate--if you're just here on a study abroad program, I would think you would have been eligible to get coverage through them for the entire period you are abroad, which would have then covered any trips you took. Perhaps if you contact them (the US branch), there would be a way they could begin coverage now, even though you've already left the country?
edited to add: sorry, I may be mixed up...if you are traveling back to the US, what I said would not apply. I assumed you meant that you were going somewhere in Europe, but realized that I may have assumed wrong.