How can I keep the momentum going on my new product launch? Sales during our announcement period were strong, and have since drastically died down

My niche brand launched a new product within a my community and got $300 of sales in the first 3 days (14 orders). Since then, things have run dry. I try to post every two days about the product, but ever since those first three days during the announcement period, I haven't gotten any sales.

Sources of advertising: I have an Instagram social media following of 2.5K followers, and a partner with 10K followers. No paid ads, all organic content (and reposts from the partner).

Am I posting too much? Am I not posting enough? I think I'll definitely need my partner with the larger following to post more, but I can't seem to figure out why sales have declined so drastically. Is this a normal thing, for brands that announce a new product? Sales are big near the announcement, then taper off over the following week?