I have an external antenna. It helps a lot, but I doubt that that is your issue. It is more likely a Telkom issue, same as with me. It happens every second month or so, and lasts anywhere from 3 days to a few weeks.
I am also on Telkom Uncapped LTE. Usually I get about 40-44Mbps. For the past week, I haven't been able to get more than 2Mbps down or up. Really frustrating, as it makes streaming impossible, and when I work, I have to kick everyone else off of the network.