Hello, it is absolutely possible that your Lexapro has stopped working as many people do report this effect where their anti-depressant seems to lose its effectiveness after a while of taking it. This leads to depression relapses and breakthrough symptoms and be very discouraging. The best course of action when this happens is to do exactly as you are - either adjust the dose to the lexapro or try something new. There are a lot of good options for antidepressants so i would stay optimistic that one of these new ones will be effective for you. Zoloft is one that is very commonly used and overall, ahs low side effects. It also has properties that affect anxiety well, much like the lexapro does, so it is a good choice for help with the anxiety (racing thoughts) and the depression.
Ride out the increase of the Zoloft and remember, full effiicacy to occur with this medicine, it usually takes 6-8 and soemtimes up to 12 weeks to accomplish so at 5, if you are toelrating it well and feeling some improvement, that is a great sign. And during the ramp up, there can be some side effects as your body adjusts. so hang in there, give this a few more weeks, and hopefully the Zoloft ends up being a suitable replacement for the Lexapro.
As far as retsrating the Lexapro, it makes sense right now to try these other options. Down the road you could try to restart the Lexapro and hope that it is effective again, but there is a good possibility it will not be.
Hope this helps! Make sure to just stay in touch with your prescribing doc about how you are feeling. There is a broad world to help with the treatment of depression from the medicine angle so something will work for you like the Lexapro did, even if it takes some tinkering with the med and dose to get there. Remember too, that if you are hacing breakthrough depression and anxiety and can recognize that things are hard on you right now or your stress is elevated, it may be a great time to get in some counseling to address the depression from two angles, giving yourself the best chance of feeling good.