Interests payments on mortgage

Hi all thanks for reading, basically I maybe being totally stupid but here goes hopefully someone can explain it to me

So I have a fixed rate mortgage with the Halifax and the last few months I have been able to see these payments online.

I have previously used a calculator online to show intrest vs capital from each of my monthly payments. This showed that as I start to pay my mortgage off each month the intrest paid will be a few pounds less and the capital paied a couple of pounds more - I hope you get what I mean?

So when i look online
My intrest part of the payments has increased so


31 May 13 Interest 321.47

30 Apr 13 Interest 312.35

31 Mar 13 Interest 240.28

I am unclear as to what this means please is this right as I thought amount of intrest would be less each month but like I said before I might have got this completely wrong

Thanks k :o:o