Agreed - this could be normal behavior; video or pics would help to say for sure.
As mentioned, you can try squid - I've heard some eels tend to really go for squid. Live food (such as live ghost shrimp or fiddler crabs) is also a good, last resort option to try and get it feeding again.
How often do you feed it? Would you say it eats more of the shrimp, more of the clams, or pretty even portions of both?
With regards to the long-term diet, I'd suggest adding a good, fatty fish like salmon (the gold-standard) or mackerel (a good, second place), squid is a good one to add, crabs too if you can do so without breaking the bank, and then I'd also add in some algae (preferably multiple types) to get a few more vitamins and minerals in there that might not be supplied by the meat.
With all the foods, the fresher the better, and the more intact the shrimp is (head, tail, shell, etc.) the better. Ulva, Halymenia, and Nori would be my first suggestions for algae to add, but others like Porphyra and Spirulina would be good too. I doubt the eel would eat the algae by itself, so supplementing it either with algae pellets (such as NLS Marine Fish Pellets), an algal gelatin feed, or through something like wrapping the meat in the algae would be my suggestion.
For more diet suggestions/info, I'd suggest reading through lion king's threads below:
Eels and lions have alot in common; I have seen many posts lately concerning eels, so I thought I would pass on some information that I have learned over the years. !st off, know your source, do not get an eel from a source that runs copper in their system. Eels have sensitivity to copper...
www.reef2reef.com
What medication was it?