My stiff shoulders give me a headache which is painful.
I have a stiff neck and shoulders which often leads to a headache. It's awful.
ーMy stiff shoulders give me a headache which is painful.
「肩こりからくる頭痛が辛い」
stiff shoulders で「肩こり」
to give me a headache で「頭痛を与える・（主語が原因で）頭痛になる」
painful で「辛い・痛い」
ーI have a stiff neck and shoulders which often leads to a headache. It's awful.
「首と肩がこってよく頭痛になるから辛い」
to lead to a headache で「頭痛の原因となる・頭痛を引き起こす」
awful で「ひどい・気分が悪い」
ご参考まで！
I get headaches from tight shoulders, and it’s really painful.
I get headaches from tight shoulders, and it’s really painful.
My headaches are caused by shoulder tension, and it’s been rough.
My shoulders are so stiff that they give me headaches.
I have a headache every day because of neck and shoulder stiffness.
「肩こりからくる頭痛が辛い」は、英語だと 肩こり（shoulder tension / tight shoulders / stiff shoulders）が原因で 頭痛（headaches）が起きている、と原因→結果で言うと自然です。
カナダ 
アメリカ合衆国 
