It's been 8 wks since my last period, previous were 7 wks, 4, 4, 4 wks apart. I've done 2 tests over the last 4 wks both negative. Should I get checks?

Yes you should. . Persistently changing periods sometimes reflect home moral abnormalities and needs to be looked at. I don't think it is going to be a big problem but still it needs to be evaluated. .