Are you holding the strinigs down with the very tips of your fingers?

I've got big shovel hands and I can get them in a line for an open 'A'....

If not, as suggested you can barre all three strings with 1 finger, or look into full barre if you fancy a challenge:

A Major

E |--5--
B |--5--
G |--6--
D |--7--
A |--7--
E |--5--

Use your index finger to hold down all the strings at the 5th fret, then use the others to hit the extra notes. You will probably find this harder, but if you've got big hands and the right kind of strength, it might be worth a whirl. It's what you'll be aiming at after the open chords anyway...