I have mapped my internal server to Public IP, it is accessible from the external network but is not accessible from the internal network. How could I access Public IP from internal network?

If you use MT as a DNS serer, you can add a private IP to your DNS server.
When you are hope and do a lookup of myserver.dyddns.org it respond with IP 192.168.88.50
And when you use a public DNS, you get your outside IP.

Smells like hairpin nat here.

With description, images and everything: http://wiki.mikrotik.com/wiki/Hairpin_NAT

I do have several web server on different ports and on different host, I would recommend a combination of DNS server and a reverse proxy server like HAProxy.

From Outside
You add a DNS pointer to your outside IP.
MT dos nat port 80 to your proxy server.
Proxy server sends you to the correct server.
Eks webcam on port 8080
Web server on port 80
Management server on port 80
etc

From Inside
Add DNS entry on your DNS to point to Proxy server.