The slight push/pull you feel when being passed by large trucks is normal as is the movement you felt with the cross winds. Sounds to me like you did pretty well for the first trip and the conditions you were driving in. The oncoming trucks are no concern at all as I have never felt anything from them. It is the ones approaching from behind that get you.
I would certainly get one of the sway control hitches. The two you mentioned are good as are several others on the market. There is a ton of discussion about sway control on this forum.
Sway control hitch discussions.In looking at your picture, it does look like you are a bit tongue high on the trailer. I would turn the shank around so it points down to the ground and see what happens. I would still use the top two holes for mounting the hitch head. I think that should lower the tongue just about enough. If not, you will still have several more holes to play with.
Hope this helps. :)
Here is your picture. I copied your url and pasted it into our forums
picture posting app.Barney