Looking for feedback of people that had to switch from one medication to another

So I have been diagnosed with MS 2 and half years ago. Right after, my doctor recommended to start treatment with Natalizumab and so I did. But right now after this period of almost 3 years taking it, honestly I feel like my body is at its limit, it's almost like it's rejecting the medication. Two months ago after my last MRI i had terrific news, the size of my brain lesions significantly decreased. But now that I'm facing those new complications, I'm a little lost honestly. I really don't know how to move on. Im sorry for any possible misspellings, English is not my first language. Any kind of support is appreciated! And thanks in advance for anyone that's reads this.