First of all, I ask you that how are you so much sure about 'Sehr' or the Shaikh who told you about it? `it may have another cause, maybe a misunderstanding or anything else. The first thing is that you should talk with your husband and try to find out the real cause and issue. You may take help of your elders in this regard.
But if all the efforts become unsuccessful and he is not ready to change his behavior then you can ask him to give you divorce but this is the last step and as you know better that divorce is the most unliked halaal act near Almighty Allah. So please avoid it as far as possible.
Although if there is no option except divorce then ask him for divorce. If he does not agree for simple divorce, ask him for a special type of divorce which is called in Islamic Term 'Khula.' In this type of talaq, when a woman doesn't like to continue her marital relationship with a man but the man wants to continue the relations, she offers him some amount to give divorce. The detailed Ahkam of Talaq-e-Khula are mentioned in Risala-e-Tauzeehul Masael.
After all if he is not agree at any condition then contact to you Marja or his representative in your area because they only have power to give onesided divorce from your side.
Kindly keep in your mind my Sister that this way is not recommended in Islam as far as other ways may be sought and applied and don't believe easily on these type of asuumptions that someone has done sehr against you. Even though as a precaution you should write this dua on a paper and always keep it with you. It's recommend by Hazrat Ali a.s. and mentioned in the famous book of dua and Amaal 'Mafateehul Jinan' of Shaikh Abbas Qummi.
بِسمِ الله وَ بِالله، بِسمِ الله وَ ما شاءَالله، بِسم الله لاحَولَ ولاقُوّه الا بالله، قالَ موسی ما جِئتُم بِه السِّحرُ اِنَّ اللهَ سَیُبطِلُهُ اِنَّ اللهَ لا یُصلِحُ عَملَ المُفسِدینَ، فَوَقَعَ الحَقُّ و بَطَلَ ما کانُوا یَعمَلونَ فَغُلِبوا هُنالِکَ وَانقَلَبُوا صاغِرینَ
Don't believe on just imaginations and illusions and don't be skeptic or obsessional untill you find a solid proof of sehr.