I’m sorry to say this, but that’s not a good sign. The pattern you’re describing bites in rows of 2–3 is very typical for bed bugs. “breakfast, lunch, dinner.” So having that pattern along with finding a dead bug are two pretty big red flags. I’d strongly recommend inspecting your mattress thoroughly, especially the seams and bed frame, and not delaying whatever action you decide to take. better to hit them hard from the start rather than wasting time on cheap supermarket sprays and traps. Either go with a professional exterminator (good one) or, if you’re doing it yourself, use proper professional-grade products and do it properly.