I often suffer from mouth ulcers. It happens in lips and on my tongue. I bite tongue and lips and I fear its caused by tooth paste. Please explain.

Stop using. Stop using the tooth past if did not goaway see your dentist to chek your bite.
Canker sores. A common ulcer of the mouth is the apthous ulcer or canker sore. They are usually small circular lesions with a white center and a red outline. They are quite painful and usually last 7-10 days. They are from a virius that resides in the nerves to you mouth. Different stresses can bring them out like anxiety, acidy food and drink and yes, some toothpastes . See your dentist for treatment.
Test theory. You can test your theory. Some people are very sensitive or allergic to ingredients in some toothpastes. Stop using your current toothpaste and see if you stop getting those ulcers. Then resume using that toothpaste & see if the ulcers return. In that way you will know for sure. Try toms toothpaste. Also see your dentist to diagnose the ulcers and help in diagnosis and prevention and\or treatment.
Debacterol. Either use debacterol or see your dentist for laser treatment.
Stress related. What you are describing sounds like recurrent apthous ulcers. They usually are stress related but whitening toothpastes can also contribute. Try changing your toothpaste to something mild like sensodyne or crest. I prescribe a paste to be placed on the lesions 4 times per day and they usually resolve in about two days. You can try otc med abrevia. If this persists see your dentist.
Stress. Stress, weakened immune system, and diet all play important role in apthous ulcers, try laser treatment or use debacterol.