Hey I get blocked on the same sounds! Even my name starts with one of those hard "kuh" sounds so it's pretty difficult. The thing thats helped me the most is by trying to make the kuh sound as soft as possible, and remember to breathe before and after you say the word! I'd block so bad I'd run out of breath so remembering to breathe helped me a lot. Hope this little bit helps I'm short on time so I can't write more!