Help! My emails are delayed or not arriving at all

So, whenever I try to send over some photos or docs from my tablet or phone, my email either just straight up doesn't show up, or it takes like... two whole hours to actually hit my inbox.

The weird thing is, if I just send a quick little note through the Android app, everything works perfectly fine—it arrives right away. But the second I attach a document or some pictures? Total meltdown with the lag.

Does anyone have any ideas or maybe some advice? I'm wondering if this might be an issue with the Gmail app itself, or what?

I remember this one time I was trying to transfer some photos from my phone over to my PC, and my computer just completely tanked—like, everything started lagging like crazy... To be honest, even now, I haven't a clue why that happened.