Is this normal – when I add a new post the others get smaller in font

I’m not sure why this is happening. On my site – which I’m still working on https://www.mindfulparentscommunity.com I currently have 2 post (I also like to use the more button in the post as that is supposed to help with SEO) – all is fine with the world. When I add a third post – the first one at the bottom of the page gets smaller – especially the title of that post – the font is now very small. If I dare add the more button to the new post – the entire home page goes all screwy – sidebars on the bottom of the page – some things in huge font, others in tiny font. Help me – why do bad things happen to good bloggers (I just made that up!)

Thanks!