I wonder if I can say 'I douted constantly whether it was correct"
The WR dictionary has no problem with itCorrectness is an odd word. Do you mean accuracy or something else?
From the beginning I doubted whether it was correct.
The correct way to structure a sentence (most especially when writing, as compared to speaking), is to place the setting (ie. time frame or context) first, and the conclusion last. Should you have a ‘time frame’ and ‘context’ in the same sentence, the time frame should come first (it makes the rest of the sentence easier to follow).I had my doubt about its correctiness all along/ from the (very) beginning/all the time
‘whether or not’ is an a shortened (and the common/only) way to say“all along, I had my doubts about (as to/regarding) whether or not it was correct”
. The phrase is used when there is some ‘doubt’ as to the idea <eg accuracy/correctness/courage/loyalty etc> of something.‘whether it was correct, or whether it was not correct’
This is a funny one in English…it depends on what the person wants to emphasise. If the person wants to emphasise the ‘consistency’ of a doubt, then you would say ‘doubted constantly’ but if you want to emphasise a ‘doubt’ that was consistent, then you would say ‘constantly doubted’…either way is understood.“I doubted constantly whether (or not) it was correct”