First off, I am so sorry about your loss. It sounds like your son was very close to you & it is perfectly normal to miss him very deeply.
The Lexapro sounds like a good first step. It is a mild anti-depressant and can also be helpful with anxiety. It does take several weeks to reach it's maximum benefit but it's usually worth the wait.
Therapy is another good choice. Holidays always seem to be so hard when we are grieving loved ones. Extra counseling sessions during those times can be very helpful. You also might ask your therapist about a grief support group in your area. Many times religious organizations, hospitals & funeral homes offer such groups free of charge, or for a small donation. They are not just for people who have lost a loved one recently, but for anyone who is still grieving their loss. I think it might be worth trying to go to one session and see what you think. The members tend to be very kind and supportive. They will let you cry when you need to cry and still want to spend time with you. Which brings me to my final point: spend time with others. Maybe it's too soon to have outright celebrations, but a quiet cup of tea with a dear friend can go a long way towards healing the soul. Try to set up at least one time every week when you can sit down in front of a friend (or someone from the support group) and spend time together. You don't need to talk. You don't need to pretend everything is okay. You just need the company. It helps.
And know that we always welcome your posts here. There are many wonderful, caring people here on HW and they will go out of their way to share whatever peace, kind words or encouragement they have to offer. We have a few members who have also lost children & they may be along, in time, to offer their own wisdom. I hope you find here renewed faith and peace and I wish you blessings on your healing journey.
peace & prayers,