How can i treat white spot?

hi i have had my tank set up with fishies for approx 2 years ive just added some different ones to make it more livlier so now have 2x tetras ( did have 6 but the others died ages ago) 3 x frogs ( 1 ive had for months but have just this week added 2 new ones) 1 sucker fish ( did have 2 but the other died 2 days ago ..had bite marks so i guess they fought to the death) i have 4 tiger barbs and 3 guppies (2 female and 1 male)the guppies i got from my sister as they got pregnant (shock horror) so she piled me off with a mating pair! (i cant wait! lol) the problem is i check my fish everyday as ive always had some problem or another and yesterday they were totally fine but today my 2 female guppies have white spot ..one is pregnant for sure .. did the stress of pregnancy cause the white spot? will they die? will she give birth still? as far as i can see none of the other fish have it yet.thanks any answer would be appreciated as long as its useful! thanks :)