male or female guinea pig?

Question
I have a 2year old male guinea pig and because his brother died recently I bought two baby guinea pigs as he looked quite depressed.One of the babies hasnt been taking to the older one so I put the other little one with the bigger one tonight for a little while.Thats when I began to wonder the sex of the little one because the bigger one began chasing the little one and tried humping him.Im not sure if its a dominance thing or not because the little one kept hiding behind the hut and the bigger one started scratching frantically at the side because he couldnt get into him.
Ive had the little ones about two weeks now.Would it be obvious if one was pregnant by now?Its difficult to check their sex becasue they are still very nervous and I dont want to make them worse.Also is there a way to make the other little one accept the bigger one?Please help me!Thanks
Dee

Answer
I have a great website for you to help with the sexing (determining the gender) of a guinea pig! It is www.cavyspirit.com/sexing . I think that it is a great website for determining the gender of a guinea pig because it has not only text but pictures to help make sure you have the correct gender (Piggy Porn ;)! )
Also I do not recommend putting an undetermined gender of guinea pig in a cage with a pull grown male for the first time EVER. One, they could fight so if you do do this, have a medium sized towel ready to throw over the older pig, this will not hurt them but confuse them long enough for you to pick him up and the little pig to hide. Two, pregnancy IS a possibility, and a hassle, and dangerous. So I do not recommend it unless you have all the information.
As for the pregnancy thing, if they had 'humped' for long enough than usually a pregnancy would not show until about 2 months after.
And to help your guinea pigs get more acquainted I would recommend doing what I did. Depending on how you are housing them (the same cage with a divider or two separate cages)I say let them be close enough to talk but have a barrier so there will be nose touching, not bum humping. Try putting a piece of lettuce in the cage bars so that one half is in with the younger pigs and the other with the older pig so that they are sharing it. And remember that lots of free time between the three of them is great, but with supervision. This has worked for me and my three girls.
As for the humping, if they are the same gender than my girls do it to. From time to time I will be in my office and I will look over a there cage and Gypsy will be doing either a mating dance or chasing and humping poor little Shadow. So no worry's if you have a little same sex mating going on between the guineas, its normal for guinea pigs.

Thanks for asking!
-Nicky