This is another ‘on the button’ question - well done 
This one tripped me up too.
Welsh is different to English in this respect.
There are a group of verbs which use the ‘was’ tense to create the past tense. You will get to know them very quickly but they tend to be verbs which imply a state of mind, for example…
Meddwl - to think
Gwybod- to know (something)
Nabod- to know (someone)
Eisiau or moyn- to want
Hoffi - to like
Gobeithio - to hope
Caru- to love
Casau- to hate
Swnio- to sound
They are called stative verbs.
Rich 